Preparation Steps

• Preheat oven to 350°F (175°C). Grease and flour a 9-inch round cake pan.
• In a large bowl, whisk together flour, sugar, cocoa powder, baking soda, and salt.
• In a separate bowl, whisk together eggs, buttermilk, vegetable oil, and vanilla extract.
• Add the wet ingredients to the dry ingredients and mix until just combined. Stir in the hot water until the batter is smooth. The batter will be thin.
• Pour the batter into the prepared cake pan and bake for 30-35 minutes, or until a wooden skewer inserted into the center comes out clean.
• Let the cake cool in the pan for 10 minutes before inverting it onto a wire rack to cool completely.
• For the dark chocolate mousse: Melt the bittersweet chocolate in a double boiler or microwave. Let it cool slightly. In a separate bowl, whip 0.5 cup of heavy cream with 1 tablespoon of sugar until stiff peaks form. Gently fold the whipped cream into the cooled melted chocolate.
• For the milk chocolate mousse: Melt the milk chocolate. In a separate bowl, whip 1 cup of heavy cream with 0.5 tablespoon of sugar until stiff peaks form. Gently fold the whipped cream into the cooled melted milk chocolate.
• For the white chocolate mousse: Melt the white chocolate. In a separate bowl, whip 1 cup of heavy cream with 0.5 tablespoon of sugar until stiff peaks form. Gently fold the whipped cream into the cooled melted white chocolate.
• Once the cake is completely cool, place it on a serving plate. Pour the dark chocolate mousse over the cake, spreading it evenly. Refrigerate for 15-20 minutes until set.
• Carefully pour the milk chocolate mousse over the set dark chocolate layer, spreading evenly. Refrigerate for another 15-20 minutes until set.
• Finally, pour the white chocolate mousse over the milk chocolate layer, spreading evenly. Refrigerate for at least 1 hour (or until firm) before serving.