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

In a medium mixing bowl, whisk together flour, cocoa powder, baking powder, baking soda, and salt. Set aside.

In a large mixing bowl, beat softened butter and sugar until light and fluffy. Add in eggs one at a time, vanilla, dry ingredients, and buttermilk until just combined.

Pour the batter into the prepared pan and bake for 25-30 minutes or until a toothpick comes out clean. Cool in the pan for 10 minutes, then transfer to a wire rack.

Puree the raspberries with sugar, strain, then whip heavy cream with vanilla until soft peaks form. Fold in melted chocolate and raspberry puree. Refrigerate to set.

Once cooled, slice the cake in half horizontally. Spread mousse on the first layer, add the second layer, and cover the entire cake with remaining mousse. Chill for at least 1 hour.

For ganache, heat heavy cream until steaming, pour over chopped chocolate, let sit, and stir until smooth. Drizzle over the chilled cake before serving.