Create the Brownie Base: Preheat your oven to 350°F (175°C). In a double boiler, melt the unsweetened chocolate and butter together until smooth. Stir in the granulated sugar, then whisk in the eggs one at a time, incorporating the vanilla extract. Combine the flour, cocoa powder, and salt in another bowl, then gradually fold the dry ingredients into your wet mixture until just combined. Pour this luscious batter into a greased 9-inch round cake pan and bake for about 25 minutes. Let it cool completely in the pan.
Prepare the Mousse Layer: For the first mousse layer, bloom the gelatin in water and let it sit for about 5 minutes. Melt the semisweet chocolate in a double boiler until just melted and allow it to cool slightly. In a mixing bowl, whip the cold heavy cream with 2 tablespoons of granulated sugar until soft peaks form. Gently fold the melted chocolate into the whipped cream, followed by the bloomed gelatin mixture. Carefully pour the mousse over the cooled brownie layer and refrigerate for at least 2 hours, or until set.
Make the Ganache Topping: Once the mousse is firm, it’s time for the crowning glory. In a saucepan, heat the additional heavy cream until it just begins to simmer, then remove it from the heat. Stir in the chopped semisweet chocolate and butter, mixing until the ganache becomes smooth and shiny. Allow it to cool slightly before pouring it over the set mousse layer. Return the cake to the fridge for another hour to allow the ganache to set perfectly.
Notes
Ensure your ingredients are at room temperature for better mixing. Don’t skip the chilling time for the best texture.