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

In a medium bowl, whisk together the all-purpose flour, cocoa powder, baking powder, baking soda, and salt.

In a large mixing bowl, beat the softened butter and sugar until light and fluffy.

Add eggs one at a time, mixing well after each addition, then stir in the vanilla extract.

Gradually alternate adding the dry ingredients and buttermilk into the butter mixture.

Pour the batter into the prepared cake pan and bake for 25-30 minutes.

Allow the cake to cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.

Puree fresh raspberries with sugar in a blender and strain through a fine mesh sieve.

Whip the heavy cream with vanilla extract until soft peaks form, then fold in melted dark chocolate and raspberry puree.

Chill the raspberry mousse for 30 minutes, then slice the cooled cake in half horizontally.

Spread half of the raspberry mousse on the first layer, then place the second layer on top.

Chill the assembled cake in the refrigerator for at least one hour.

Heat heavy cream in a small saucepan until just boiling, then pour over chopped dark chocolate and stir until smooth.

Drizzle the ganache over the chilled cake and serve with whipped cream and raspberries.