Layered chocolate mousse cake

Ingredients:

Brownie

• 0.5 cups premium flour
• 1/4 cup cocoa powder
• 1/4 cup sugar
• 5 tbsp. milk
• 4 tbsp unsalted butter, melted
• 0.5 tsp vanilla extract
• 1 large egg
• Special equipment: springform pan with a diameter of 22 cm.

Mousse

• 165 g unsalted butter
• 3/4 cup cocoa powder + extra for sprinkling
• 4 cups heavy cream
• 1 packet (7 g) of gelatin
• 1 cup of sugar
• 1 tbsp vanilla extract

Ganache

• 1 and 1/4 cups heavy cream
• 4 tablespoons unsalted butter
• 340 g semi-sweet chocolate, chopped

Preparation:

1. Preheat oven to 350°F (175°C) and spray the bottom of a 9-inch springform pan with cooking spray.
2. Brownie:
   
   In a medium bowl, combine the flour, cocoa powder, and sugar. Stir in the milk, butter, vanilla extract, and egg until smooth. Pour the batter into the prepared pan and bake until a knife inserted into the center comes out clean, about 20 minutes. Cool completely on a wire rack, about 30 minutes.
3. Open the pan lock, remove the ring, and spray it with cooking spray. Line the ring with a 6-cm-wide strip of parchment paper, making sure it fits snugly against the sides. Reattach the ring to the bottom of the pan with the cake.
4. Mousse:
   
   Coarsely chop 4 tablespoons butter and place in a medium microwave-safe bowl. Microwave in 30-second intervals, stirring, until melted, about 1 minute. Add 1/4 cup cocoa powder, stir until smooth, and set aside. Cut the remaining 8 tablespoons butter and place in a medium microwave-safe bowl. Microwave in 30-second intervals, stirring, until melted, about 1 minute. Add the remaining 1/2 cup cocoa powder, stir until smooth, and set aside.
5. Pour 1/4 cup heavy cream into a small microwave-safe bowl and stir in the gelatin. Let sit for 5 minutes to soften the gelatin. Microwave in 30-second intervals, stirring, until the gelatin dissolves, about 1 minute. Let cool to room temperature, about 5 minutes.
6. Transfer the gelatin to the bowl of a stand mixer fitted with a whisk attachment and add the sugar, vanilla extract, and the remaining 3 3/4 cups heavy cream. Beat on medium speed until stiff peaks form, 3-4 minutes. Divide the whipped cream into two large bowls. Fold one bowl of the cocoa powder-butter mixture into each portion of whipped cream and mix until there are no streaks (one bowl will have dark chocolate mousse, the other will have light chocolate mousse).
7. Spoon the dark chocolate mousse over the brownie pans. Smooth the surface with an offset spatula. Spread the light chocolate mousse over the dark mousse and smooth the surface with an offset spatula. Refrigerate until the mousse is completely set, at least 3 hours or overnight.
8. Ganache:
   
   In a small saucepan over medium heat, bring the heavy cream and butter to a simmer. Place the semisweet chocolate in a large heatproof bowl and pour the hot cream over it. Let it sit for 5 minutes, then stir until smooth and glossy.
9. Open the pan lock and remove the ring and parchment paper from the sides of the cake. Smooth the edges with a hot, dry spatula. Place a wire rack on a rimmed baking sheet and set the cake on the rack. Pour the ganache over the cake, letting it drip down the sides until it covers the entire cake. Run a clean, large offset spatula over the surface of the cake once to smooth it out. Refrigerate for 30 minutes.
10. Holding a stencil or other perforated surface (like a napkin or lattice) over the cake, sprinkle generously with cocoa powder to create a pretty pattern (do not place the stencil on the cake). Serve immediately.