Chocolate Cake Recipe

Prepare and preheat

Preheat oven to 350°F (175°C). Grease and line two 8-inch (20 cm) round cake pans with parchment paper; grease the parchment as well.

Mix dry ingredients

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

Combine wet ingredients

In a separate bowl, whisk the eggs, milk, vegetable oil, and vanilla extract until well blended.

Make the batter

Pour the wet mixture into the dry ingredients and stir until just combined. Gradually add the boiling water while stirring slowly — batter will be thin; this produces a moist cake.

Bake

Divide batter evenly between prepared pans. Bake in the preheated oven for 25–30 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs. Rotate pans halfway through baking for even rise.

Cool

Allow cakes to cool in pans for 10 minutes, then run a knife around edges and invert onto wire racks. Remove parchment and cool completely before assembly (about 1 hour).

Bloom gelatin

Sprinkle the instant gelatin over the 2 tbsp cold water in a small bowl and let sit 2–3 minutes to bloom.

Melt chocolate

Chop the 10 oz semi-sweet chocolate and place in a heatproof bowl. Heat 1 cup (240 ml) of the heavy cream until just simmering and pour over the chocolate. Let sit 1 minute, then stir until smooth. Stir in the hazelnut paste and the 2 tablespoons granulated sugar until fully incorporated. Stir in the bloomed gelatin and the 2 tbsp oil or melted butter until glossy and smooth. Let the chocolate mixture cool to lukewarm (about 15–20 minutes).

Whip cream

Whip the remaining 2 cups (480 ml) heavy cream to medium peaks (soft peaks that hold shape but are still pliable).

Fold mousse

Gently fold one-third of the whipped cream into the cooled chocolate-hazelnut mixture to lighten it, then fold in the remaining whipped cream in two additions until uniformly blended. Be careful not to deflate the mixture; the mousse should be light and airy.

Chill

Place mousse in the refrigerator to firm slightly while you prepare the glaze and cake layers (15–30 minutes).

Make glaze

Chop the 6 oz chocolate and place in a bowl. Heat 3/4 cup heavy cream with the corn syrup until just simmering. Pour hot cream over the chocolate and let sit 1 minute, then stir until completely smooth. Stir in the tablespoon of butter until glossy. If glaze is too thick to pour, warm gently over a double boiler or microwave in 10-second bursts until pourable but not hot. Let cool to a slightly warm pourable temperature (about 90°F / 32°C).

Level and layer

If cake layers have domes, level the tops with a serrated knife. Place one cake layer on a cake board or serving plate. Spread about half of the hazelnut chocolate mousse evenly over the first layer with an offset spatula, leaving a small edge. Smooth the mousse.

Second layer

Place the second cake layer on top and press lightly. Spread the remaining mousse over the top, smoothing to the edges. For a clean look, you can pipe a thin rim of mousse around the top edge to hold the glaze.

Chill to set

Refrigerate the assembled cake for at least 30 minutes to 1 hour to firm the mousse so the glaze will set cleanly.

Glaze the cake

Place the chilled cake on a wire rack set over a sheet pan to catch excess glaze. Pour the slightly warm glaze over the center of the cake, letting it run and cover the top and sides. Use an offset spatula to encourage even coverage if needed. Allow excess glaze to drip off. Return cake to refrigerator for the glaze to set, about 15–20 minutes.

Garnish and serve

Carefully transfer cake to serving platter. Sprinkle chopped toasted hazelnuts around the top edge or center and scatter chocolate shavings. Let the cake sit 10–15 minutes at room temperature before slicing for cleaner cuts. Slice with a sharp knife warmed under hot water and wiped dry between cuts.