Chocolate Mousse Cake Recipe

Prepare and Preheat

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

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

In a large bowl or stand mixer bowl, whisk together the granulated sugar, eggs, milk, oil, and vanilla until smooth and slightly foamy (about 1–2 minutes).

Gradually add the dry ingredients to the wet mixture and mix on low speed until just combined, scraping the bowl once. Do not overmix.

Fold in the hot brewed coffee slowly until the batter is smooth and slightly thin. The coffee intensifies the chocolate flavor.

Pour the batter into the prepared pan(s) and smooth the top with a spatula. Bake for 22–28 minutes for one 8-inch layer (or 18–22 minutes for thinner layers) until a toothpick inserted near the center comes out with a few moist crumbs.

Let the cake cool in the pan on a wire rack for 15 minutes, then remove from pan and cool completely on the rack. If using a springform, after 15 minutes invert onto rack, peel parchment, and right-side up to finish cooling.

Melt chocolate and butter: Place the chopped semi-sweet chocolate and 2 tablespoons butter in a heatproof bowl. Set over (not in) simmering water (double boiler) or microwave in 20–25 second bursts, stirring between, until smooth. Let cool slightly (to about 100–110°F / warm to the touch).

Whisk egg yolks and sugar: In a small bowl, whisk the egg yolks with the 1/4 cup granulated sugar until pale and slightly thickened (about 1–2 minutes). Temper the yolks by adding 2 tablespoons of the warm melted chocolate mixture while whisking, then pour the tempered yolks back into the rest of the chocolate and mix until smooth. Stir in the 1/8 tsp salt and 1/2 tsp vanilla.

Whip cream: In a chilled bowl with chilled beaters, whip the 1.5 cups cold heavy cream to soft peaks (starts to hold shape but still silky).

Fold: Gently fold one-third of the whipped cream into the chocolate-yolk mixture to lighten it, then fold in the remaining cream in two additions until fully combined and smooth, keeping as much air as possible. Do not overfold or deflate.

Chill: Cover the mousse and refrigerate for at least 30 minutes to set slightly so it holds together during assembly (longer is fine; up to 4 hours).

Heat the cream: Place 1/2 cup heavy cream in a small saucepan and heat to just simmering — bubbles form at the edge but do not boil — or microwave until steaming.

Pour over chocolate: Put the 6 oz finely chopped semi-sweet chocolate in a heatproof bowl. Pour the hot cream over the chocolate and let sit for 1–2 minutes to melt. Add softened butter and optional corn syrup.

Emulsify: Stir gently from the center outward until the ganache is smooth, glossy, and homogenous. Cool at room temperature until thickened but still pourable (about 15–20 minutes). If it becomes too stiff, warm gently in short bursts.

Level and layer cake: If you baked one thick cake, slice horizontally into two even layers with a long serrated knife. Place the bottom layer on a cake board or serving plate. If you used two pans, place one layer down.

Spread mousse: Spoon or pipe half of the chilled mousse onto the bottom cake layer and spread evenly to the edges with an offset spatula, leaving a small gap at the edge if you want a ganache drip. Smooth the surface.

Chill to set: Place the cake with the mousse layer in the refrigerator for 15–30 minutes to slightly firm the mousse so the top layer won't sink.

Add top cake layer: Place the second cake layer gently on top of the mousse, pressing lightly to level. Chill 10 minutes.

Pour ganache: When the ganache has cooled to a pourable but slightly thickened consistency, pour it over the top of the cake, starting in the center and spreading toward the edges with an offset spatula so it coats the top and slightly runs down the sides. Use a spoon to encourage even drips if desired.

Finish: Smooth the sides or leave natural. Dust the top lightly with 1 teaspoon unsweetened cocoa powder and scatter chocolate shavings if using. Return the cake to the refrigerator for at least 1 hour to fully set the mousse and ganache.

Serve: Remove from refrigerator 10–15 minutes before serving for best texture. Slice with a hot, dry knife (wipe between cuts) to get clean slices.