Preheat your oven to 350°F (175°C). Grease a round cake pan and line the bottom with parchment paper for easy release.

In a large mixing bowl, sift together the all-purpose flour, cocoa powder, baking powder, and salt.

In another bowl, beat the softened butter and granulated sugar until light and fluffy (about 3-4 minutes).

One by one, add the eggs, mixing well after each addition. Stir in the vanilla extract until well combined.

Gradually add the dry mixture to the wet ingredients, mixing just until combined.

Pour the batter into the prepared cake pan and bake for 30-35 minutes, or until a toothpick comes out clean. Allow it to cool completely.

Chop the dark, milk, and white chocolate and melt each using a double boiler or microwave.

In a separate bowl, whip the heavy cream until soft peaks form. Divide this whipped cream into three bowls and fold in the respective melted chocolate.

Once the cake has cooled, slice it horizontally into three equal layers. Spread each layer with the respective mousse.

Allow the cake to chill in the refrigerator for at least 4 hours or overnight. Decorate with chocolate shavings or fresh berries before serving.