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

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

Cream the softened butter and granulated sugar using a mixer for about 3-5 minutes until light and fluffy. Add eggs one at a time, mixing well, followed by vanilla extract.

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

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

Allow the cake to cool in the pan for 10 minutes before transferring to a wire rack to cool completely.

For the mousse, puree fresh raspberries with sugar, strain to remove seeds, then whip heavy cream until soft peaks form and fold in raspberry puree and melted chocolate.

Once the cake is cool, slice it into two layers, spread half the mousse on the first layer, place the second layer on top, and spread the remaining mousse over the top.

Chill the cake in the refrigerator for at least 1 hour.

To prepare the ganache, heat cream until just boiling, then pour over the chopped chocolate, stirring until smooth.

Drizzle the ganache over the chilled cake, slice, and serve.