Set your oven to 350ºF and prepare an 8-inch springform pan by applying nonstick spray and lining it with parchment paper, making sure to spray the paper as well.

Melt the unsweetened chocolate and butter in a medium saucepan over medium-low heat, stirring until the mixture is smooth, then add the sugar and let it cool slightly.

Once it's only slightly warm, blend in the eggs and vanilla extract until everything is combined. Sift the flour, cocoa powder, and salt over the mixture and fold gently using a spatula.

Transfer the brownie batter into the prepared pan and bake for 20 to 25 minutes, until a toothpick comes out with a few moist crumbs, then cool completely in the pan or chill in the fridge for a quick cooldown.

For the mousse, hydrate the gelatin in water for about 5 minutes. In a saucepan, warm ½ cup of heavy cream and 2 tablespoons of sugar until it simmers, remove from heat, stir in the gelatin, and pour over chopped semisweet chocolate. Stir until smooth and cool to room temperature.

Whip the remaining 1 cup of heavy cream until it reaches medium to stiff peaks. Carefully mix in one-third of the cream into the chocolate mixture, then fold in the rest until no streaks are left.

Spread the chocolate mousse over the cooled brownie layer and chill while preparing the ganache.

In a saucepan, heat the remaining cream and butter, removing it from the heat just before it begins to boil. Pour this mixture over the rest of the semisweet chocolate, stirring until melted and smooth.

Once cooled to room temperature, pour the ganache over the mousse layer and let it set in the refrigerator for about an hour. Once set, carefully release the sides of the springform pan, remove the parchment, and transfer to a serving platter. Enjoy with whipped cream or fresh berries!