Preheat your oven to 350°F (175°C) and grease and flour two 9-inch round cake pans.

Whisk together the all-purpose flour, granulated sugar, unsweetened cocoa powder, baking powder, baking soda, and salt in a large bowl.

In another bowl, combine buttermilk, vegetable oil, eggs, and vanilla extract until smooth.

Pour the wet mixture into dry ingredients and stir gently until just combined.

Gradually stir in boiling water until smooth.

Divide the batter between prepared pans and bake for 30-35 minutes or until a toothpick comes out clean.

Let cakes cool in the pans for 10 minutes before transferring to wire racks to cool completely.

In a saucepan, cook fresh raspberries, sugar, and lemon juice over medium heat until thickened.

Bloom gelatin in cold water and stir into warm raspberry puree until dissolved.

Whip heavy cream until stiff peaks form and fold in the raspberry mixture.

Place one cake layer on a serving plate, spread raspberry mousse over it, and add the second layer.

Refrigerate for at least 2 hours to allow mousse to set.

For the ganache, heat heavy cream until simmering and pour over chopped dark chocolate, then mix in unsalted butter until smooth.

Pour ganache over the mousse cake and decorate with fresh raspberries, chocolate shavings, and dust with powdered sugar.

Chill assembled cake for an additional 30 minutes before serving.