Preheat your oven to 350°F (175°C). Grease and line an 8-inch springform pan with parchment paper. In a medium saucepan, melt together unsweetened chocolate and unsalted butter over low heat, stirring until smooth. Remove from heat and mix in granulated sugar. Next, whisk in eggs and vanilla extract. Sift in flour, cocoa powder, and salt, mixing until just combined. Pour the batter into the prepared pan and bake for 20-25 minutes, or until a toothpick comes out with moist crumbs. Allow to cool completely.

While the brownie base cools, prepare the mousse filling. In a small bowl, sprinkle gelatin powder over cold water and let it bloom for about 5 minutes. In a saucepan, heat heavy cream and granulated sugar until just simmering. Remove from heat and add the bloomed gelatin, stirring until dissolved. Pour this mixture over chopped semisweet chocolate and stir until completely smooth. Let the mixture cool slightly before folding in whipped cream in two additions. Spread the mousse over the cooled brownie base and refrigerate for at least 2 hours to set.

Once the mousse is set, prepare the glossy ganache. In a small saucepan, heat heavy cream and butter until just about to boil. Remove from heat and pour it over chopped semisweet chocolate, stirring until completely melted and smooth. Allow the ganache to cool slightly, then pour it over the set mousse layer, spreading it evenly. Return the cake to the refrigerator for another hour to set the ganache.

After the ganache has fully set, carefully remove the cake from the springform pan by releasing the sides. Slice into generous pieces and serve each slice with a dollop of whipped cream or fresh berries, allowing everyone to indulge in the rich layers of the Triple Chocolate Mousse Cake. Enjoy!