This super moist dark chocolate mousse cake combines unsweetened natural cocoa powder and dark cocoa powder for an extra rich flavor. Fill the cake with a simplified chocolate mousse and cover the whole dessert with semi-sweet chocolate ganache. If needed, you can prepare the ganache and mousse ahead of time.
My s’mores chocolate mousse inspired me to play around in the kitchen the other week. I’ve always loved chocolate mousse, back to my childhood when my mom served it as an easy (yet totally elegant) dessert on the holiday table. Chocolate mousse is simple divinity in its own right, but when paired with chocolate cake, it’s downright decadent.
I made this chocolate mousse cake for my husband Kevin’s birthday. This cake basically demands a huge gathering because—trust me—you don’t want to be left alone with its temptation. It WILL call out your name each time you open the refrigerator.
Taunting you.
3 Parts to Dark Chocolate Mousse Cake
Let’s break down each component of this intensely rich cake:
- Dark Chocolate Cake: This is actually a variation of my tuxedo cake, which originated from my chocolate cake recipe. In recent years, I’ve found that replacing sour cream for some of the buttermilk gives the cake more structure.
- Chocolate Mousse: I researched simplified ways to make a fluffy chocolate mousse filling without the use of eggs or gelatin. This chocolate mousse filling combines real chocolate and homemade whipped cream. Or our whipped frosting would make a wonderful alternative filling if you don’t want to make the chocolate mousse!
- Chocolate Ganache: Top the whole cake with 2 ingredient semi-sweet chocolate ganache. You should be a chocolate ganache pro by now!
Video Tutorial: Chocolate Mousse Cake
Stick-to-the-back-of-your-fork moist. This is every chocolate lover’s dream!
Dark Chocolate Cake
Use this chocolate cake as the starting point. For a sturdier, yet moister crumb, swap some sour cream in for the buttermilk and reduce the hot liquid. The acidity in both sour cream and buttermilk is a must to properly leaven this cake. (If desired, see my posts on Baking Powder vs Baking Soda and Baking with Buttermilk for more information.) This cake has a natural dark chocolate taste, but to deepen that flavor, use a mix of natural cocoa and Hershey’s Special Dark cocoa powder. A touch of espresso powder and hot coffee further enhances the chocolate flavor. The cake will not taste like coffee. Rather, the two add depth to the cake’s chocolate flavor.
- Why hot liquid? The hot liquid encourages the cocoa powder to bloom and dissolve. If you don’t drink coffee, you can use hot water.
You have options! You can make this cake into 2, 3, or 4 layers. I highly recommend 3 or 4 layers because there’s over 4 cups of chocolate mousse to spread inside. You can use 8 inch or 9 inch pans. The bake times are similar, see recipe notes.
A cup of chocolate chips adds even more chocolate flavor. I used 1 cup (180g) of mini semi-sweet chocolate chips in this pictured cake, but left them out in the video. They’re optional, but definitely worth the addition!!
You can also see this exact cake batter baked as three layers in both my chocolate peanut butter cake and chocolate raspberry cake (try one of those next!).
Simplified Chocolate Mousse
The chocolate mousse adds a creamy and light contrast to the dark chocolate layers. You need 6 ingredients:
- Hot Water
- Cocoa Powder – natural or dutch-process
- Melted Chocolate – use two 4-ounce chocolate baking bars found in the baking aisle
- Heavy Cream
- Confectioners’ Sugar
- Vanilla Extract
Whisk the hot water and cocoa powder together. Pour into melted chocolate. The hot water breaks up the chocolate, adding to the airy mousse consistency. Cocoa powder creates additional chocolate flavor. Fold this chocolate mixture into whipped cream—a combination of heavy cream, confectioners’ sugar, and vanilla extract.
Whipped cream + our chocolate mixture. ↑
Fold them together to make our chocolate mousse filling. ↓
Baker’s Tip: The chocolate mousse must chill in the refrigerator before using, so it’s a good idea to make it ahead of time or as the chocolate cake layers are cooling. The mousse is best cold, so I actually recommend serving the cake cold. (Additionally, the cake is much easier to assemble if the mousse is cold!)
By the way, this chocolate mousse also makes for a wonderful alternate filling in homemade eclairs!
Chocolate Ganache
I won’t go into a lot of detail about the chocolate ganache because I have a complete chocolate ganache tutorial for you! Like the chocolate mousse, it’s imperative to use pure chocolate. Wait about 20 minutes for the ganache to thicken before pouring onto the cake.
How to Assemble & Decorate Chocolate Mousse Cake
Chocolate ganache enrobes 4 cake layers and 3 mousse layers. Place bottom cake layer on your cake stand or serving plate. Using a large icing spatula, evenly cover the top with about 1.5 cups of chilled chocolate mousse. Top with 2nd cake layer and another 1.5 cups of mousse. Top with the third cake layer, then spread another 1.5 cups mousse evenly on top. (Save a large spoonful of mousse for a thin crumb coat.) Top with final 4th cake layer. Spread any remaining mousse around the sides as a crumb coat. Run a bench scraper around the cake to smooth it out. Refrigerate cake for at least 1 hour and up to 4 hours. Chocolate mousse is pretty fluffy, so the cake won’t hold its shape unless it’s properly chilled.
Pour ganache on top then run a bench scraper around the sides to smooth it out. You can serve the cake immediately or wait for the chocolate ganache to set. 🙂
What About Cupcakes?
Instead of a big cake, you can make chocolate mousse cupcakes. Use my chocolate cupcakes recipe and halve the chocolate mousse and chocolate ganache recipes below. Fill the cupcakes with chocolate mousse using my Sugar Plum Fairy Cupcakes as an example. Drizzle cooled cupcakes with ganache. Eat your heart out!
You can also use the chocolate mousse instead of pastry cream in homemade mille-feuille!
More Indulgent Chocolate Desserts
- Dark Chocolate Bread Pudding
- German Chocolate Cake
- Flourless Chocolate Cake
- Black Forest Cake
- Chocolate Lava Cakes
- Chocolate Mousse Pie
- Mint Chocolate Cake
Dark Chocolate Mousse Cake
- Prep Time: 2 hours, 30 minutes (includes chilling)
- Cook Time: 25 minutes
- Total Time: 5 hours, 55 minutes (includes cooling)
- Yield: serves 12
- Category: Cake
- Method: Baking
- Cuisine: American
Description
This super moist dark chocolate cake combines unsweetened natural cocoa powder and dark cocoa powder for an extra rich flavor. Fill the cake with a simplified chocolate mousse and cover it with semi-sweet chocolate ganache. If needed, you can prepare the ganache and mousse ahead of time. See notes.
Ingredients
- 1 and 3/4 cups (219g) all-purpose flour (spooned & leveled)
- 3/4 cup (62g) unsweetened natural cocoa powder* (see note)
- 1 and 3/4 cups (350g) granulated sugar
- 2 teaspoons baking soda
- 1 teaspoon baking powder
- 1 teaspoon salt
- 2 teaspoons espresso powder (optional)*
- 1/2 cup (120ml) canola or vegetable oil
- 2 large eggs, at room temperature
- 3/4 cup (180g) full fat sour cream, at room temperature
- 1/2 cup (120ml) buttermilk, at room temperature*
- 2 teaspoons pure vanilla extract
- 1/2 cup (120ml) hot water or coffee*
- optional: 1 cup (180g) mini or regular semi-sweet chocolate chips
- optional garnish: fresh berries and/or chocolate shavings
Chocolate Mousse
- 1/2 cup (120ml) hot water
- 1/4 cup (22g) unsweetened cocoa powder* (see note)
- two 4-ounce quality semi-sweet chocolate bars (113g each), finely chopped*
- 2 cups (480ml) heavy cream or heavy whipping cream
- 2 Tablespoons (15g) confectioners’ sugar
- 1/2 teaspoon pure vanilla extract
Chocolate Ganache
- two 4-ounce quality semi-sweet chocolate bars (113g each), finely chopped*
- 1 cup (240ml) heavy cream or heavy whipping cream
Instructions
- Preheat oven to 350°F (177°C). Grease four 8-inch or 9-inch cake pans, line with parchment paper rounds, then grease the parchment paper. Parchment paper helps the cakes seamlessly release from the pans. (If it’s helpful, see this parchment paper rounds for cakes video & post.)
- Make the cake: Whisk the flour, cocoa powder, sugar, baking soda, baking powder, salt, and espresso powder (if using) together in a large bowl. Set aside. Using a handheld or stand mixer fitted with a whisk attachment (or you can use a whisk) mix the oil, eggs, and sour cream together on medium-high speed until combined. Add the buttermilk and vanilla and mix until combined. Pour the wet ingredients into the dry ingredients, add the hot water/coffee, and whisk or beat on low speed until the batter is completely combined. Fold in the chocolate chips, if using.
- Divide batter evenly between 4 pans. Bake for 19-23 minutes. Baking times vary, so keep an eye on yours. The cakes are done when a toothpick inserted in the center comes out clean.
- Remove the cakes from the oven and set on a wire rack. Allow to cool completely in the pan. The cakes may slightly sink in the middle as they cool—that’s expected.
- As the cakes cool, prepare the chocolate mousse so it can chill and be ready at the same time as the cake layers. You can also prepare the mousse 1-2 days ahead of time. Whisk the hot water and cocoa powder together. Set aside. Melt the chopped chocolate bars in a double boiler or use the microwave. If using the microwave: place the chopped chocolate in a medium heat-proof bowl. Melt in 20 second increments in the microwave, stirring after each increment until completely melted and smooth. Pour hot water/cocoa mixture into melted chocolate and stir until thick and smooth. Set aside. Using a hand mixer or a stand mixer fitted with a whisk attachment, whip the heavy cream, confectioners’ sugar, and vanilla extract together on medium-high speed until medium peaks form, about 3-4 minutes. Medium peaks are between soft/loose peaks and stiff peaks. Pour in the chocolate mixture and using a spoon or rubber spatula, gently fold together. Avoid over-mixing which can deflate/thin out the mousse. Cover mousse and chill in the refrigerator for at least 2 hours and up to 2 days. Makes about 4.5 cups chocolate mousse.
- Assemble layers before preparing chocolate ganache: First, level the cakes if needed: using a large serrated knife, slice a thin layer off the tops of the cakes to create a flat surface. Discard (or crumble over ice cream!). Place 1 cake layer on your cake stand, cake turntable, or serving plate. Using a large icing spatula, evenly cover the top with about 1.5 cups chocolate mousse. Top with 2nd layer and evenly cover the top with 1.5 cups chocolate mousse. Top with the third cake layer, then spread another 1.5 cups mousse evenly on top. Save a large spoonful of mousse for a thin crumb coat. Top with final 4th cake layer. Spread any remaining mousse around the sides as a crumb coat. Run a bench scraper around the cake to smooth out crumb coat. Refrigerate cake for at least 1 hour and up to 4 hours. Prepare the ganache as you wait.
- Chocolate Ganache: Place chopped chocolate in a medium heat-proof bowl. Heat the cream in a small saucepan over medium heat until it begins to gently simmer. (Do not let it come to a rapid boil– that’s too hot!) Pour over chocolate, then let it sit for 2-3 minutes to gently soften the chocolate. With a metal spoon or small rubber spatula, very slowly stir until chocolate has melted and mixture is smooth. The finer you chopped the chocolate, the quicker it will melt with the cream. If it’s not melting, do not microwave it. If needed, see Troubleshooting Chocolate Ganache. Once ganache mixture is smooth, let it cool for 20 minutes at room temperature before spreading on chilled cake.
- Pour/spoon ganache on chilled cake. Smooth the top with an icing spatula and the sides with a bench scraper. Top with optional garnish such as fresh berries and/or chocolate shavings. Serve cake immediately or chill, uncovered, for up to 4-6 hours before serving. Cake can be served at room temperature or chilled.
- Cover leftover cake tightly and store in the refrigerator for 5 days.
Notes
- Make Ahead & Freezing Instructions: Prepare cake through step 4. Wrap the individual baked and cooled cake layers tightly and refrigerate for up to 2 days or freeze up to 3 months. Bring to room temperature, make mousse filling, then continue with step 6. You can prepare the chocolate mousse in advance. See step 5. You can also prepare the chocolate ganache ahead of time too. Refrigerate prepared ganache for up to 2-3 days. Bring to room temperature before spreading onto cake. Frosted cake freezes well, up to 3 months. Thaw overnight in the refrigerator, then bring to room temperature or serve cold.
- Special Tools (affiliate links): 8-inch Round Cake Pans or 9-inch Round Cake Pans | Glass Mixing Bowl | Whisk | Electric Mixer (Handheld or Stand) | Cooling Rack | Double Boiler | Cake Stand or Cake Turntable | Large Icing Spatula | Bench Scraper | Cake Carrier (for storage)
- 3 Layer Cake: You can also prepare this cake as a 3 layer cake. Divide batter between three 8-inch or 9-inch cake pans in step 1 and bake for 22-25 minutes or until a toothpick inserted in the center comes out clean. Use about 2 cups of chocolate mousse between each layer.
- Espresso Powder/Coffee: Espresso powder and coffee will not make the cake taste like coffee. Rather, they deepen the chocolate flavor. I highly recommend them both. If coffee isn’t your thing, you can leave out the espresso powder and use extra hot water instead of the hot coffee.
- Cocoa Powder: For the best dark chocolate flavor in the cake, I recommend using a blend of unsweetened natural cocoa powder (1/4 cup; 22g) and Hershey’s “Special Dark” cocoa powder (1/2 cup; 43g). Hershey’s Special Dark is actually a mix of natural cocoa powder (an acid) and dutch-process cocoa powder (a base) and it worked fine in this recipe. This recipe needs acidic natural cocoa powder, so do not use ALL dutch-process cocoa powder. For best results, use 3/4 cup (65g) natural or the blend of natural/Special Dark I used. For the chocolate mousse, you can use either unsweetened natural or dutch-process cocoa powder. (Or the Hershey’s Special Dark.)
- Why Room Temperature? All refrigerated items should be at room temperature so the batter mixes together easily and evenly. Read more about why room temperature ingredients are important. Instead of sour cream, you can use plain yogurt. The cake won’t taste as rich, but it’s a fine substitute.
- Buttermilk: Buttermilk is required for this recipe. You can make your own DIY buttermilk substitute if needed. Add 1 teaspoon of white vinegar or lemon juice to a liquid measuring cup. Then add enough whole milk to the same measuring cup until it reaches 1/2 cup. (In a pinch, lower fat or nondairy milks work for this soured milk, but the cake won’t taste as moist or rich.) Stir it around and let sit for 5 minutes. The homemade “buttermilk” will be somewhat curdled and ready to use in the recipe.
- Chocolate in Mousse & Ganache: Mousse & ganache will only set if the correct chocolate is used. You can use high quality chocolate chips if needed (I prefer Ghirardelli semi-sweet chocolate chips), but I recommend using pure chocolate baking bars. You can find them right next to the chocolate chips in the baking aisle. They are sold in 4 ounce bars. I like Bakers or Ghirardelli brands.
Hi! I am thinking of using your chocolate mousse recipe to fill a vanilla cake and frost it with buttercream. Would the cake need to be refrigerated overnight or can it sit out at room temp? Thanks!!
Hi Antoni, with the mousse, we’d recommend refrigerating overnight. Enjoy!
Hi there,
This cake looks so delicious. My sister is having twins, and her birthday is right after her due date, so I’m making her birthday cake, and she requested this one. She lives about an hour away. Do you think this cake would travel ok?
Hi Shannon, as long as the cake has been sufficiently chilled before traveling, that should work just fine. Hope it’s a hit!
If you want an absolutely divine, heavenly, exquisite, gourmet cake, then this Dark Chocolate Mousse Cake is for you! I make this cake for special occasions and it’s a hit every single time. The only problem is, the mousse and ganache taste SO GOOD by themselves, that I keep sampling them, hoping I’ll have enough left over for the cake!
Can this cake be fully frosted and refrigerated the previous day before serving? Will it turn hard? can i serve it directly from
the fridge or should it come to room temperature? please help with your reply
Yes. Refrigerate it overnight, and then, for best taste and texture, I would let it sit at room temperature for about 1 hour before serving.
Can I use chocolate buttercream icing instead of chocolate ganache?
Hi Janet, yes, but the cake will be much sweeter. I recommend ganache for best results.
Hi Sally, what would be the recommended baking time and temperature if using 6” round baking pans
Hi Paul, For a 6-inch cake, we’d recommend using this chocolate cupcakes recipe as the batter to make a 3 layer 6 inch cake. See our 6 inch cake recipes post as a guide. Halve the chocolate mousse and ganache from this recipe so there’s just enough. Hope this helps!
Sally, I prepared the cake, three 10” layers. I have the buttercream in the fridge. It’s creamy but I know it will firm up in the fridge. The mousse is very light. How does the mousse as layer filling support the weight of the cake? I’m concerned I’ll make a mess and have to assemble this Thursday morning for a 60th birthday!!! Help!
Hi Pam, you’ll want to bring the ganache coating to room temperature before attempting to spread on the cake. The mousse holds up the cake well in this recipe on its own, but feel free to use cake dowels for extra support if you wish!
Thanks! It went quite well.
DON’T make this cake unless you want everyone who has a bite request that you make it for every special occasion for the rest of time:) I do FOUR layers and follow the recipe exactly and it has come out perfectly every time and I’ve already made at least 10 of these cakes. FABULOUS!!
OMG! This cake is absolutely divine! It’s a chocolate lover’s dream. The chocolate mousse is heavenly. I made it for my niece’s bday and ended up making a four-layer cake. There were no leftovers. I don’t need any other chocolate cake recipe. This is it! Definitely the best! Thank you for sharing!
This is a great recipe! So delicious. My husband doesn’t really eat sweets, except chocolate chip cookies, and he ate a whole piece by himself! That says it all! It’s easy, just time consuming. I will definitely make this again!
Looking to make my step-dad a chocolate cake for his birthday and think this is the winner! He loves chocolate cake and mousse. However, I’m thinking of coating the outside with chocolate buttercream instead of chocolate ganache (we are big fans of icing in this house) – would that still give enough structure? Also concerned it might be overly sweet…what do you think?
Hi Kelsey, it will certainly be sweet, but I think it will still be wonderful. Especially since the chocolate mousse filling isn’t overly sweet. The cake will still have enough structure and be stable when layered and complete.
What can I use instead of sour cream, heavy cream and the buttermilk for a non-dairy version?
Hi CG, we haven’t tested a dairy-free version of this recipe, but let us know if you do any experimenting.
Hi Sally! First wanted to say I absolutely love this recipe. It is a favorite in my family now and constantly requested for birthdays! My brother asked if I could make it for his big 30th birthday this weekend, but I would need to double it and so I’m thinking of doing it in a 13×9 sheet cake pan. Any advice on cook time and all of that would be greatly appreciated. Thanks!
Hi Megan, you can make this recipe as a 9×13-inch sheet cake (same oven temperature, about 35-40 minutes bake time). We’re so glad this cake is a hit with your family!
Hi Sally, just wanted to thank you for this recipe, since I first made it years ago, it’s still every family members request that I make one for each of their birthdays!! We all love the intense chocolate flavour, but not too sweet with the simple ganache, and mousse. I feel like a professional baker when I create this cake in my kitchen – I omit the chips, but otherwise follow your recipe and it never lets me down! For anyone wanting to try, I highly recommend this cake recipe to satisfy any chocolate lovers dream!
Hi, I made this last week and it was delicious! The only thing me & my family found too intense in flavour was the addition of the chocolate ganache. I am planning to make this cake again next week for my son’s birthday party however I’m concerned about it going very soft if I don’t add the ganache on the outside. Do you think just coating the cake with chocolate mousse on the outside will be enough to give the cake stability? I need to transport the cake in the car to the party (about 10min) and worried that the cake layers might ‘slide’ as the mousse goes quite soft when left out. I will refrigerate the cake as soon as we get to the party and plan on serving it chilled.
Thank you for a wonderful and easy to follow recipe!
Hi Marina, a few readers have reported success doing so! You may wish to use cake dowels for extra support. Glad the cake was a hit!
Hi Sally, can I bake this on a sheet pan? What should be the temperature setting and baking time? I love your recipes
Hi Ginny, You can make this recipe as a 9×13-inch sheet cake (same oven temperature, about 35-40 minutes bake time).
Hi Sally, I like in UK and we don’t seem to have semi-sweet chocolate.. could I replace this with milk chocolate or 50/50 milk/dark?
Also, could I use self raising flour instead of plain flour?
Thank you!
Hi Marina, yes, you could use milk chocolate or 50/50—just be sure that they are still pure baking chocolate bars. We do not recommend self raising flour here, since they have varying amount of leavening in them. Best to use all-purpose here. Hope you enjoy the cake!
I was trying to figure out if the chocolate mixture needs to sit to cool before adding the whipped cream for the mousse. I would think if still hot it would just melt the whipped cream, so how long should it sit before adding the whipped cream to it?
Hi Sherri, the chocolate mixture should cool just enough while you’re making the whipped cream mixture. If it still seems excessively hot, you can let it cool for another 5 minutes.
Can you use butter instead of vegetable oil?
Hi Karen, using butter here would yield a dry cake. Best to stick with oil for chocolate cakes!
Why do you not use eggs in the choc mousse sally
Hi Divya, this is a “simplified” version of mousse compared to other recipes that use eggs or gelatin.