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

Whisk together all-purpose flour, cocoa powder, baking powder, baking soda, and salt in a bowl.

In a large bowl, beat the softened butter and sugar until light and fluffy for 3 to 5 minutes.

Add the eggs to the butter mixture one at a time, mixing well after each addition and then stir in the vanilla.

Gradually alternate adding the dry mix and buttermilk, starting and ending with the dry mix, mixing until just combined.

Pour the batter into the prepared pan, smoothing the top, and bake for 25 to 30 minutes.

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

Puree fresh raspberries with sugar, strain, then whip the heavy cream until soft peaks form and fold in the raspberry puree and melted chocolate.

Chill the raspberry mousse in the refrigerator for about 30 minutes.

Once the cake is cool, slice it in half, spread mousse on the bottom layer, then place the top layer and cover with remaining mousse.

Cover and refrigerate the assembled cake for at least 1 hour.

For the ganache, heat cream until simmering, pour over chocolate, let sit, then stir until smooth and drizzle over the chilled cake.