Dark Chocolate Mousse Cake
Rich but perfectly balance chocolate cake layers with an easy dark chocolate mousse. The most delicious chocolate cake you will ever have.
Ingredients
Chocolate Mousse
- ½ cup hot water
- ¼ cup (22 grams) dutch-processed cocoa powder
- 8 oz. semi-sweet chocolate bars finely chopped
- 2 cups heavy cream cold
- 2 Tablespoons confectioner's sugar
- ½ teaspoon vanilla extract
Cake Layers
- 1¾ cups (220 grams) all-purpose flour
- ½ cup (43 grams) dutch-processed cocoa powder
- ¼ cups (22 grams) natural cocoa powder
- 1½ cups (323 grams) granulated sugar
- 2 teaspoons baking soda
- 1 teaspoon baking powder
- 1 teaspoon kosher salt
- 1 teaspoons espresso powder
- 2 large eggs at room temperature
- ½ cup neutral oil avocado or canola
- ¾ cup sour cream at room temperature
- ½ cup buttermilk at room temperature
- 2 teaspoons vanilla extract
- ½ cup hot coffee
Chocolate Ganache
- 6 oz. semi-sweet chocolate finely chopped
- ¾ cup heavy cream
Instructions
Chocolate Mousse
- In a small bowl, whisk the hot water and cocoa powder together until smooth. Set it aside.
- Melt the chopped chocolate either in a double boiler or in the microwave in short bursts. Once it’s completely smooth, stir in the hot water/cocoa mixture with a rubber spatula. It should turn silky and glossy. Set it aside to cool.
- In the bowl of a stand mixer, add the heavy cream, confectioner’s sugar, and vanilla. Using the whisk attachment, whip on medium-high speed until medium peaks form.
- Pour the melted chocolate mixture into the bowl of whipped cream. Gently fold it together with a rubber spatula, making sure to scrape the bottom so everything gets incorporated. Stop as soon as the streaks disappear—overmixing will deflate the mousse.
- Cover the bowl with plastic wrap and refrigerate at least overnight so it can set.
Chocolate Cake Layers
- Grease three or four 8-inch cake pans and line the bottoms with parchment.
- In a medium bowl, whisk together the flour, cocoa powders, sugar, baking soda, baking powder, salt, and espresso powder. Set aside.
- Preheat your oven to 350°F.
- In a large bowl, whisk together the oil, eggs, sour cream, buttermilk, and vanilla.
- Add the dry ingredients to the wet ingredients, and as you whisk, slowly pour in the hot coffee. Mix until everything is just combined. The batter will be very thin.
- Divide the batter evenly between the pans and bake for 15–20 minutes, or until a toothpick comes out with just a few moist crumbs.
- Let the cakes cool completely on a rack before removing them from the pans.
Assembly
- Once the cakes are cooled, run a butter knife around the edges, flip them out, and peel off the parchment.
- Take the mousse out of the fridge and divide it into equal portions—three if you baked three layers, four if you baked four layers.
- Place a small dollop of mousse on your cake board or stand to keep the first layer in place. Set the first cake layer down and spread one portion of mousse evenly over the top with an offset spatula. Repeat with the remaining layers, placing the final cake layer upside down so the top is nice and flat. If the mousse gets too soft while you build the cake, just pop everything into the fridge for a few minutes.
- Use the last portion of mousse to give the whole cake a thin crumb coat. Refrigerate while you prepare the ganache.
Chocolate Ganache
- Place the chopped chocolate in a heatproof bowl.
- Warm the heavy cream in a small saucepan until it just starts to simmer. As soon as it does, remove it from the heat and pour it over the chocolate. Let it sit for 2–3 minutes, then stir until smooth. Let the ganache cool slightly to room temperature, but don’t let it firm up., about 15 minutes.
- Remove the cake from the fridge and pour the ganache over the top. Work fairly quickly to smooth it out and create drips down the sides if you like a rustic look. For a neater finish, use a bench scraper or icing spatula to smooth the sides. Add berries or chocolate shavings on top if you’d like.
- Refrigerate the cake for at least 6 hours before slicing. You can serve it chilled straight from the fridge or let it warm up for about 30 minutes for a softer texture.
Notes
TIPS FOR SUCCESS
- Read the recipe before you start so you can plan around the chill times. It’s written in the order I recommend making each component.
- Make the mousse the day before if you can—it needs several hours to set.
- Room-temperature ingredients really matter here. Sour cream and buttermilk need time to warm up. If you forget about the eggs, you can place them in warm water for a few minutes.
- If this is your first time, use three 8-inch pans instead of four. Four layers are gorgeous, but they’re thinner and trickier to stack until you get the hang of it.
- Only the mousse requires the mixer. When you're done whipping the cream, just pop the mixer bowl into the fridge until you're ready to assemble.
- Finely chopped chocolate melts faster and smoother—worth the extra effort.
- Use good-quality baking chocolate. Skip chocolate chips; they don’t melt well because of their stabilizers.
- The cake layers can be made ahead. Wrap cooled layers tightly in plastic, place in a zip-top bag, and refrigerate for 1 day or freeze for up to a month. Cold layers are actually easier to stack. Avoid leveling these cakes—they’re super soft and may crumble.
- If stacking gets messy or your mousse starts softening, just stop and chill everything. Cooler mousse = better structure. A bench scraper makes straightening the sides easy once you’re back at it.
- If you want the cake to stay fresh longer—or you’re making it for a special event—coat the whole thing in ganache. It locks in the moisture beautifully. A simple drip is fine too if you prefer less fuss.
- Keep the cake refrigerated until about 30 minutes before serving.
- Add toppings (berries are my favorite) right after smoothing the ganache. Once the ganache sets, toppings won’t stick well. This cake is rich, so the tartness of fresh berries really balances it.