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

In a medium bowl, whisk together all the dry ingredients: all-purpose flour, unsweetened cocoa powder, baking powder, baking soda, and salt until there are no clumps.

In a large mixing bowl, beat the softened butter and granulated sugar together using an electric mixer on medium speed for about 3–5 minutes until light and fluffy.

Gradually add the eggs one at a time, mixing well after each. Stir in the vanilla extract until combined.

Slowly mix the dry ingredient blend into your wet ingredients while adding the buttermilk. Fold until just combined.

Pour the cake batter into the prepared pan, smoothing the top, and bake for 25–30 minutes or until a toothpick comes out clean. Let cool in the pan for 10 minutes before transferring to a wire rack.

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

Once the cake has cooled, slice it in half horizontally. Spread half of the mousse on one layer and place the second layer on top, spreading the remaining mousse on top.

Cover with plastic wrap and chill in the refrigerator for at least 1 hour for the mousse to set.

For the ganache, heat heavy cream until just simmering and pour it over the chopped dark chocolate. Stir until smooth.

Remove the cake from the refrigerator, drizzle ganache over the top, and garnish with fresh raspberries.