Chocolate Mousse Cake Recipe

Prep

Preheat oven to 350°F (180°C). Lightly grease and line the bottom of a 9-inch (23 cm) springform or round cake pan with parchment.

In a medium bowl whisk together flour, cocoa powder, sugar, baking powder, and salt until evenly combined.

In a separate small bowl whisk egg, milk, oil, and vanilla until smooth.

Pour wet ingredients into dry and stir gently until just combined. Batter will be thin — do not overmix.

Pour batter into prepared pan, smoothing the top. Bake for 10–12 minutes or until a toothpick inserted near center comes out with a few moist crumbs. Remove from oven and cool in pan on a rack for 10 minutes, then transfer to wire rack to cool completely. Once cool, trim or level top if necessary and return to the pan (or use a removable-bottom pan) for mousse assembly.

Chop the 200 g chocolate into small even pieces and place in a heatproof bowl.

Heat 1/2 cup of the heavy cream in a small saucepan until it just begins to simmer (do not boil). Pour the hot cream over the chopped chocolate and let sit 1 minute, then stir until smooth to make a chocolate ganache. If using espresso powder, stir it into the hot cream before pouring over the chocolate so it dissolves.

In a small bowl whisk the egg yolks with 2 tablespoons sugar until pale and slightly thickened.

Temper the yolks: add about 2 tablespoons of the warm chocolate ganache to the yolks while whisking to raise their temperature, then whisk the yolk mixture back into the remaining chocolate ganache until fully combined and smooth. Add 1/8 tsp salt (or use the 1/4 tsp from ingredients) and mix.

Chill the remaining 1.5 cups heavy cream until cold, then whip it to soft-medium peaks. Reserve about 1/3 cup of whipped cream for glazing (if desired) and fold the rest gently into the cooled chocolate-yolk mixture in two additions, keeping as much air as possible. Stop folding when no streaks remain and the mousse is uniform and airy.

Spoon or pipe the mousse over the cooled sponge in the pan, smoothing the top with an offset spatula. Tap gently on the counter to remove large air pockets. Refrigerate the cake for at least 3 hours, preferably overnight, until mousse is set.

Place the 80 g chocolate in a heatproof bowl and bring 1/2 cup heavy cream to a simmer. Pour hot cream over the chocolate and let sit 1 minute, then stir until smooth. Add the butter and stir until glossy and combined. If glaze is too thick after cooling, warm gently over a double boiler to reach a pourable but not hot temperature (about 90–95°F / 32–35°C).

Remove the cake from the refrigerator about 10–15 minutes before glazing to take the chill off. Unlock and remove the springform side if used; keep the cake on the base. Place a wire rack over a tray and set the cake on the rack. Pour the glaze in the center and spread quickly with an offset spatula to encourage an even coat, letting excess drip into the tray. Use reserved 1/3 cup whipped cream to smooth edges or fix minor imperfections if needed.

Transfer the glazed cake to a serving plate using a wide spatula. Refrigerate for 15–30 minutes to let the glaze set slightly before serving.

Dust the top lightly with cocoa powder using a fine sieve, leaving room for any berries or shavings.

Arrange fresh berries or sprinkle chocolate shavings around the edge or in the center as desired. Keep refrigerated and serve chilled; remove from fridge 10–15 minutes before slicing for easiest cutting.