Chocolate Mousse Cake Recipe

Prepare pan and oven

Preheat oven to 350°F (175°C). Grease and line the bottom of an 8-inch (20 cm) springform or round cake pan with parchment paper; grease sides.

Combine dry ingredients

In a medium bowl sift or whisk together 0.75 cups all-purpose flour, 0.25 cups unsweetened cocoa powder, 1 tsp baking powder and 0.25 tsp salt until uniform.

Mix wet ingredients

In a large bowl, whisk 3 large eggs with 0.75 cups granulated sugar until slightly thickened and pale (about 2–3 minutes by hand or 1–2 minutes with a mixer). Add 3 tbs vegetable oil, 3 tbs milk and 1 tsp vanilla extract; whisk to combine.

Combine batter

Fold the dry ingredients into the wet mixture gently until just incorporated. Do not overmix to keep sponge light.

Bake

Pour batter into prepared pan and smooth top. Bake in preheated oven 15–18 minutes, or until a toothpick inserted near the center comes out with a few moist crumbs. The layer should be thin (about 3/4 inch).

Cool

Remove cake from oven and let cool in pan on a rack 10 minutes. Run a knife around the edge, then invert onto rack and peel off parchment. Allow to cool completely. If needed, trim to fit the base of your springform ring (8-inch).

Melt chocolate

Chop 8 oz bittersweet chocolate finely and place in a heatproof bowl. Heat about 0.5 cup of the heavy cream until just simmering (do not boil) and pour over chocolate. Let sit 1 minute, then whisk until smooth. If using, whisk in 1 tbs unsalted butter and 1/8 tsp salt. Set aside to cool to lukewarm.

Whip remaining cream

Pour remaining 1 cup heavy cream into a chilled bowl and whip to soft peaks (stiff but still spreadable). Cover and refrigerate briefly if it becomes too soft while you finish other steps.

Beat egg whites

In a clean dry bowl, whip 2 room-temperature egg whites with 2 tbs granulated sugar until glossy stiff peaks form. The meringue should hold a peak but not be dry.

Combine chocolate and cream

When melted chocolate is lukewarm, fold one large spoonful of whipped cream into chocolate to lighten it. Then fold in the rest of the whipped cream gently with a spatula until uniformly pale and airy.

Fold in meringue

Gently fold the beaten egg whites into the chocolate-cream mixture in three additions, using a light hand to preserve air. Work quickly but gently until homogeneous and mousse is airy.

Assemble cake

Place the cooled sponge layer into the bottom of the springform pan or keep it on the serving plate and fit an 8-inch cake ring around it. Spread the chocolate mousse evenly over the sponge, smoothing the top. Tap the pan gently on the counter to remove large air pockets.

Chill to set

Cover with plastic wrap and refrigerate at least 4 hours, ideally overnight, until mousse is fully set and sliceable.

Prepare topping

About 15 minutes before serving, whip 0.5 cup cold heavy cream with 1 tbs powdered sugar and 0.5 tsp vanilla extract to soft peaks.

Release and garnish

Run a warm knife around the springform sides to loosen and remove the ring. Pipe or spoon whipped cream on top and dust with 1 tbs cocoa powder or scatter chocolate shavings for garnish.

Serve

Use a hot, dry knife (wipe between slices) to cut clean slices. Serve chilled. Leftovers can be refrigerated up to 3 days.