This indulgent chocolate mousse cake recipe is for real chocolate lovers. The cake is soft and moist, with a rich chocolate flavor. It has a very light texture and can be served with whipped heavy cream or fresh berries.
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Ingredients and substitutes
Eggs - Eggs can be right from the fridge because we're going to warm them in a double boiler with sugar before whipping.
Sugar - You can use white granulated sugar or castor sugar both for sponge as well as for simple syrup.
Flour - We need all-purpose flour or cake flour to make this dark chocolate cake recipe.
Cocoa powder - You will need Dutch-processed cocoa powder (unsweetened).
Vanilla extract and salt - These are extra flavorings for the chocolate genoise sponge. I also like to add some salt to the chocolate mousse but it's optional.
Milk - Use whole milk at room temperature to make the cake layers and sugar syrup.
Fats - As always, I prefer using unsalted butter and odorless vegetable oil in almost all of my cake recipes. Butter provides a lot of flavor and oil (such as canola oil or sunflower oil) keeps the cake soft for longer.
Instant coffee - I like to use coffee to flavor simple syrup, but you can omit this ingredient completely and make it just with milk and sugar. Alternatively, replace milk with water so your syrup is flavorless. You can also use fresh-ground coffee when you cook simple syrup and pass it through a sieve after to remove the coffee grounds.
Gelatin - I used flavorless powdered gelatin from Dr. Oetker (220 bloom) that can be replaced with the same amount of powdered Knox Gold gelatin. Don't forget to bloom your gelatin in cold water before using it.
Chocolate - I use semi-sweet chocolate chips to make a chocolate ganache for the mousse.
Heavy whipping cream - Use heavy cream to make the ganache.
Mascarpone cheese - I also add some mascarpone cheese to make my mousse more creamy. You can replace it with full-fat sour cream or cream cheese.
Cooking tips
Use a tall cake pan. Chocolate genoise sponge can be baked in one cake pan and then split into two cake layers. Because the cake batter will rise a lot in the oven, you will need a 3-4" (8-10cm) tall cake pan or springform pan. Read my Genoise sponge post to learn everything you need to know about this very easy-to-make and delicious sponge that is perfect for multiple-layer cakes.
Wait until the mousse has thickened so you can pipe it. For this specific cake, it's easier to have chocolate mousse that can be piped on top of the sponge cake rather than poured on top. You can transfer the mousse into a piping bag, close it and place it in the fridge to thicken up a bit. Once you see that the mixture has reached a buttercream consistency, you can use it. If you missed the moment and your mousse became too thick to pipe, heat it in the microwave for 5 seconds at a time and and press the bag until the mixture becomes softer.
Step by step directions
For the simple syrup
1. In a saucepan, combine all syrup ingredients. Heat over medium heat just until it starts boiling.
2. Remove from the heat and pour into a bowl to cool down before using.
For the chocolate genoise sponge
1. Preheat the oven to 340F or 170C and prepare a 6” (15cm) round cake pan that is 3”- 4” tall (8-10cm) by covering the bottom with a piece of parchment paper. The sides of the pan should stay untouched!
2. In a heat-proof bowl, add the eggs, sugar, and vanilla extract. Heat the mixture over a pot with simmering water, stirring consistently, until warm to the touch and all sugar has dissolved.
3. Place the mixture in the bowl of a stand mixer fitted with a whisk attachment and whip for 7-10 minutes or until the mixture becomes very pale, has tripled in volume, and is thick enough to leave a ribbon on the surface.
4. Sieve in the flour, cocoa powder, and salt, and carefully fold with a rubber spatula until no dry ingredients are left.
5. In a small bowl add the oil, melted butter, and milk. Mix and add 2-3 tablespoons of the egg and flour mixture. Mix again until homogenous in consistency.
6. Fold the milk mixture into the main batter with the rubber spatula.
7. Pour the batter into the prepared pan and bake for 25-30 mins or until a toothpick inserted in the center comes out clean.
8. Remove from the oven and let the cake cool down until you can safely touch the pan.
9. Run a knife against the wall of the pan to release the cake. Place on a cooling rack to cool down to room temperature. Wrap in plastic wrap and refrigerate for 2-4 hours or overnight.
10. Then, slice into 2 even cake layers and assemble the cake.
For the chocolate mousse filling
1. In a small bowl, add the gelatin powder and water. Mix and set aside for 5 minutes to bloom.
2. Meanwhile, pour the heavy cream into a saucepan and heat just until it starts simmering.
3. Place the chocolate in a bowl and pour the hot cream on top. Let sit for 3 minutes, then mix with a rubber spatula until homogenous in consistency.
4. Add the mascarpone cheese and mix until fully incorporated.
5. Place a bowl with gelatin in the microwave and heat it to melt. Then, pour into the chocolate mixture and whisk to combine.
6. Cover with plastic wrap so it touches the top of the mousse and refrigerate until thick but pipeable.
7. Transfer the mousse into a piping bag, cut off the tip, and use it.
Assembling the chocolate mousse cake
1. Place the first cake layer on a plate you will use for serving and brush it with simple syrup so it is spread evenly.
2. Then, pipe approximately half of the mousse and spread it evenly on top of the first cake layer. Place the second cake layer and press gently to attach it to the mousse.
3. Brush it with the rest of the simple syrup. Then, pipe the rest of the mousse on top, leaving a little bit to apply to the sides of the cake. Frost the sides of the cake and even out the top if needed.
4. Refrigerate the cake for 2 hours. Dust the top with cocoa powder (or use shaved dark chocolate to sprinkle on top). Serve your decadent chocolate mousse cake topped with fresh berries!
Why use a simple cake syrup?
Some sponge cakes (like genoise sponge) need a little bit of help to stay moist and have a melt-in-your-mouth feeling. Simple syrup is used to soak your cake layers and even give them extra flavor by using different spices, herbs, etc.
Possible variations
Add more coffee - You can dissolve a little bit of instant coffee in heavy cream before pouring it on top of the chocolate that we use to make the mousse.
Raspberry coulis - You can use raspberry coulis (not thickened with corn starch) instead of simple syrup to bring some raspberry flavor to this chocolate dessert.
Whipped cream - You can whip heavy cream with some powdered sugar to stiff peaks and pipe it on top of our chocolate mousse cake as a simple but delicious decoration.
FAQ
Store the cake in a cake box or covered with plastic wrap on a plate in the fridge for up to 4 days.
Yes, this cake can be frozen for up to 2 months. Thaw in the fridge overnight before serving.
Yes, you can bake your cake layers 1-2 months in advance and freeze them. Thaw in the fridge overnight before assembling the cake.
If your chocolate mousse has set too early and become too hard to pipe, heat it in the microwave for 10 seconds at a time. The gelatin will melt and make your mousse softer.
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Recipe card
Chocolate mousse cake
Equipment
- Digital kitchen scale
- a 6” (15cm) round cake pan that is 3”- 4” tall (8-10cm) or a springform that is at least 3” tall
- Stand mixer or hand mixer and a large mixing bowl
- Piping bags
Ingredients
Genoise sponge
- 3 large eggs at room temperature
- 95 g white granulated sugar
- 80 g all-purpose flour
- 15 g cocoa powder
- ½ teaspoon salt
- 35 ml milk at room temperature
- 15 g unsalted butter melted
- 15 g vegetable oil
- 1 teaspoon vanilla extract
Simple syrup
- 60 g whole milk
- 1 teaspoon instant coffee optional
- 60 g sugar
Mousse
- 7 g gelatin such as Knox gold or Dr. Oetker
- 35 ml water cold
- 260 g semi-sweet chocolate chocolate chips, or finely chopped chocolate bar
- 320 ml heavy whipping cream
- 100 g mascarpone cheese
Serving
- Cocoa powder
- Fresh raspberries
Instructions
For the syrup
- In a saucepan, combine all syrup ingredients. Heat over medium heat just until it starts boiling.
- Remove from the heat and pour into a bowl to cool down before using.
For the sponge
- Preheat the oven to 340F or 170C and prepare a 6” (15cm) round cake pan that is 3”- 4” tall (8-10cm) by covering the bottom with a piece of parchment paper. The sides of the pan should stay untouched! If you don’t have such a pan, bake in two shallow cake pans or in a springform that is at least 3” tall.
- In a heat-proof bowl, add the eggs, sugar, and vanilla extract. Place over a pot with slightly simmering water. Heat the mixture, stirring consistently, until warm to the touch and all sugar has dissolved.
- Place the mixture in the bowl of a stand mixer fitted with a whisk attachment (or use a hand mixer and a bowl) and whip for 7-10 minutes or until the mixture becomes very pale, has tripled in volume, and is thick enough to leave a ribbon on the surface.
- Sieve in the flour, cocoa powder, and salt, and carefully fold with a rubber spatula until no dry ingredients are left.
- In a small bowl add the oil, melted butter, and milk. Mix and add 2-3 tablespoons of the egg and flour mixture. Mix again until homogenous in consistency.
- Add the milk mixture to the main batter and fold with the rubber spatula until fully incorporated.
- Pour the batter into the prepared pan and bake for 25-30 mins or until a toothpick inserted in the center comes out clean. If you use two pans, bake both layers at once and adjust the baking time.
- Remove from the oven and let the cake cool down until you can safely touch the pan.
- Run a knife against the wall of the pan to release the cake. Place on a cooling rack to cool down to room temperature. Wrap in plastic wrap and refrigerate for 4 hours or overnight.
- Then, slice into 2 even cake layers and assemble the cake.
For the mousse
- In a small bowl, add the gelatin powder and water. Mix and set aside for 5 minutes to bloom.
- Meanwhile, pour the heavy cream into a saucepan and heat just until it starts simmering.
- Place the chocolate in a bowl and pour the hot cream on top. Let sit for 3 minutes, then mix with a rubber spatula until homogenous in consistency.
- Add the mascarpone cheese and mix until fully incorporated.
- Place a bowl with gelatin in the microwave and heat it to melt. Then, pour into the chocolate mixture and combine.
- Cover with plastic wrap so it touches the top of the mousse and refrigerate until thick but pipeable. Can take 30 minutes to 1 hour. Check the cream often so it won’t become too thick. If this has happened, heat in the microwave for 5-10 seconds and mix with a spatula.
- Transfer the mousse to a piping bag, cut off the tip, and use it.
Assembling the cake
- Place the first cake layer on a plate that you will use for serving and brush it with simple syrup so it is spread evenly.
- Then, pipe approximately half of the mousse and spread it evenly on top of the first cake layer. Place the second cake layer and press gently to attach it to the mousse.
- Brush it with the rest of the simple syrup. Then, pipe the rest of the mousse on top, leaving a little bit to apply to the sides of the cake. Frost the sides of the cake and even out the top if needed.
- Refrigerate for 2 hours. Dust the top with cocoa powder (or use shaved dark chocolate to sprinkle on top) and decorate with fresh berries. Serve!
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