Chocolate Mousse Cake

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This French-inspired chocolate mousse cake has three layers of chocolate perfection: a moist sponge base with a coffee-cocoa soak, silky egg-free chocolate mousse stabilized with gelatin, and a thick ganache pour on top. Not too sweet, perfectly balanced, and it slices like a dream thanks to an acetate collar for sharp, clean sides.

Prep Time30

Cook Time18

Chill Time5

Total Time5 48

Course: Dessert

Cuisine: American, French

Servings: servings

Equipment

Ingredients

Chocolate Sponge Cake

¾ cup alll-purpose flour
½ cup Dutch-process cocoa powder
¼ tsp baking powder
¼ tsp baking soda
¼ tsp fine salt
⅔ cup granulated sugar
⅓ cup vegetable oil
2 large eggs room temperature
½ cup hot brewed coffee (or hot water)
¼ cup buttermilk room temperature
1 tsp vanilla extract

Coffee-Cocoa Soak

¼ cup brewed coffee warm
1 tbsp Dutch-process cocoa powder
1 tbsp granulated sugar

Chocolate Mousse

8 oz dark chocolate finely chopped
4 oz milk chocolate finely chopped
3 cups cold heavy cream divided
1 tbsp powdered beef gelatin
4 tbsp cold water
⅓ cup powdered sugar
1½ tsp vanilla extract

Chocolate Ganache

4½ oz dark chocolate finely chopped
½ cup + 2 tbsp heavy cream heavy cream
2 tsp unsalted butter room temperature

Decoration

1 chocolate bar room temperature (for curls)

US Customary - Metric

Instructions

Make the Chocolate Sponge Cake

Preheat oven to 325°F. Grease a 9-inch springform pan and line the bottom with parchment paper.
In a large bowl, whisk together the flour, cocoa powder, baking powder, baking soda, and salt.
¾ cup alll-purpose flour, ½ cup Dutch-process cocoa powder, ¼ tsp baking powder, ¼ tsp baking soda, ¼ tsp fine salt
In a separate bowl, whisk together the sugar, oil, eggs, buttermilk, and vanilla until smooth.
⅔ cup granulated sugar, ⅓ cup vegetable oil, 2 large eggs, ¼ cup buttermilk, 1 tsp vanilla extract
Pour the wet ingredients into the dry and whisk until just combined. Add the hot coffee and stir until the batter is smooth. The batter will be thin.
½ cup hot brewed coffee (or hot water)
Pour into the prepared pan. Bake for 15 to 18 minutes, until a toothpick comes out with moist crumbs. Start checking at 15 minutes.
Let cool in the pan for 5 minutes, then flip the cake upside down onto a cooling rack to flatten the dome. Cool completely. Trim any remaining dome with a serrated knife if desired.

Soak the Cake

Whisk together the warm coffee, cocoa powder, and sugar until dissolved.
¼ cup brewed coffee, 1 tbsp Dutch-process cocoa powder, 1 tbsp granulated sugar
Place the cooled cake back in the springform pan. Poke the surface all over with a fork. Brush the coffee-cocoa soak evenly over the top. Let absorb for a few minutes.
Line the inside wall of the springform pan with a strip of acetate, pressing it against the metal. Cut it slightly taller than the pan so it extends about half an inch above the rim. Tape where the ends overlap.

Make the Chocolate Mousse

Sprinkle the gelatin over the cold water in a small bowl. Let bloom for 5 minutes.
1 tbsp powdered beef gelatin, 4 tbsp cold water
Place both the dark and milk chocolate in a large heatproof bowl.
8 oz dark chocolate, 4 oz milk chocolate
In a small saucepan, heat ¾ cup (180ml) of the heavy cream until it just simmers. Remove from heat, add the bloomed gelatin, and stir until dissolved.
3 cups cold heavy cream
Pour the hot cream over the chocolate. Let sit 1 to 2 minutes, then stir from the center outward until smooth. Cool to 85 to 90°F (lukewarm to the touch).
Whip the remaining 2¼ cups (540ml) heavy cream with the powdered sugar and vanilla to medium-stiff peaks.
3 cups cold heavy cream, ⅓ cup powdered sugar, 1½ tsp vanilla extract
Fold ⅓ of the whipped cream into the chocolate mixture vigorously to lighten it. Gently fold in the remaining whipped cream in two additions until no white streaks remain.
Pour the mousse over the cake in the springform pan. Smooth the top and tap the pan gently to release air bubbles. Cover with plastic wrap (don’t let it touch the surface) and refrigerate at least 4 hours, preferably overnight.

Make the Ganache

Place the chopped chocolate in a heatproof bowl. Heat the cream until it just simmers, pour over the chocolate, and let sit 2 minutes. Stir from the center outward until smooth. Stir in the butter.
4½ oz dark chocolate, ½ cup + 2 tbsp heavy cream, 2 tsp unsalted butter
Let cool to 85 to 90°F (pourable but not hot). Remove the springform ring and gently peel away the acetate. Pour the ganache over the set mousse and tilt the pan to spread evenly. Refrigerate at least 1 hour.

Decorate and Unmold

Using a plain vegetable peeler (no plastic backing), peel long strokes along a room temperature chocolate bar to create curls. Arrange on top of the ganache.
1 chocolate bar
Refrigerate 20 to 30 minutes. Let the cake sit at room temperature 10 to 15 minutes before slicing.
Slice with a sharp knife dipped in hot water and wiped dry between each cut.

Notes

All dark chocolate option: For a more intense mousse, use 12 oz dark chocolate total and skip the milk chocolate.
Acetate substitute: If you don’t have acetate, line the pan with strips of parchment paper. The sides won’t be as clean but it works.
Gelatin adjustment: For a softer mousse, reduce gelatin to 2½ tsp. For firmer slices, increase to 1¼ tbsp.
8-inch pan: Bake the cake 2 to 3 minutes longer. The acetate should extend 1 inch above the rim.
Make ahead: Bake the cake and make the mousse up to 2 days before serving. Add ganache and chocolate curls day of.
Storage: Refrigerate 3 to 4 days. Freeze up to 1 month wrapped in plastic and foil.

Nutrition