Preheat your oven to 350°F (175°C) and prepare an 8-inch round cake pan by greasing the sides and dusting with flour.

In a medium bowl, whisk the all-purpose flour, unsweetened cocoa powder, baking powder, baking soda, and salt until well combined.

In a large bowl, beat the softened unsalted butter and granulated sugar until light and fluffy. Add eggs one at a time, then stir in the vanilla extract.

Gradually add the dry ingredients to the butter mixture, alternating with the buttermilk, mixing until combined.

Pour the batter into the cake pan and bake for 25-30 minutes, or until a toothpick inserted comes out clean.

While the cake cools, puree fresh raspberries with sugar, strain to remove seeds, then whip heavy cream and fold in melted dark chocolate and raspberry puree.

Once the cake is cool, slice it in half and spread half of the raspberry mousse on the bottom layer. Add the second layer and the rest of the mousse on top.

For the ganache, heat heavy cream until boiling, pour over chopped dark chocolate, stir until smooth, then drizzle over the chilled cake.