Preheat your oven to 350°F (175°C) and grease an 8-inch springform pan.

Melt 8 ounces of unsweetened chocolate with ½ cup of unsalted butter over simmering water.

Stir in 1 cup of granulated sugar, followed by 3 large eggs and 1 teaspoon of vanilla extract.

In another bowl, whisk together ½ cup of all-purpose flour, ¼ cup of Dutch-process cocoa powder, and ¼ teaspoon of salt.

Combine wet and dry ingredients, pour the mixture into the pan, and bake for 20-25 minutes.

Allow cooling in the pan.

Sprinkle 1 tablespoon of gelatin powder over 3 tablespoons of cold water and let it bloom for 5 minutes.

In a saucepan, heat 1 cup of heavy cream with ¼ cup of granulated sugar until dissolved.

Whisk in the bloomed gelatin, remove from heat, and pour over 8 ounces of semisweet chocolate.

Stir until smooth, allow to cool slightly, then fold in 2 cups of whipped heavy cream.

Spread the mousse over the cooled brownie base.

Heat 1 cup of heavy cream and 2 tablespoons of unsalted butter until just boiling.

Remove from heat and add 8 ounces of semisweet chocolate, stirring until smooth.

Let it cool slightly, then pour the ganache over the mousse layer.

Cover the cake with plastic wrap and refrigerate for at least 1 hour.

Once set, remove from the springform pan and slice.

Serve plain or with optional toppings like whipped cream or fresh berries.