Preheat the oven to 350 degrees. Prepare 3, 6 inch cake pans with cooking/baking spray and line the bottoms with parchment paper (trace the bottom of the pan onto parchment paper and then cut out a circle).

In a medium bowl, combine flour, sugar, cocoa powder, baking powder, baking soda and salt.

In a small bowl combine the buttermilk, oil, eggs and vanilla.

Stir the wet ingredients into the dry ingredients until just combined. Pour in the hot coffee and stir until combined.

Divide the cake batter between the 3 pans evenly. Bake for 20-22 minutes until a cake tester inserted into the middle of the cakes comes out clean. Let the cakes cool in the pans for about 15 minutes and then turn out onto a wire rack to cool completely.

Combine the raspberries, sugar and 1 tablespoon of water in a small saucepan over medium heat. Stir until the sugar fully dissolves and the raspberries soften.

Puree the raspberry mixture in a blender or food processor and then press it through a fine mesh sieve to get rid of the seeds.

Stir in the lemon juice and then pour it back into the saucepan over medium heat. Add the gelatin and bring the mixture to almost a boil while stirring constantly until the gelatin is fully dissolved. Remove it from the heat and let it cool for about 10 minutes.

Puree the raspberries in a blender or food processor until smooth. Push the puree through a fine mesh sieve to separate the seeds from the puree. Discard the seeds and set aside the puree.

In a medium bowl set over a saucepan of about 2 inches of gently boiling water that is not touching the bowl, add the egg whites and sugar.

Constantly whisk the sugar and egg whites for about 4-5 minutes until the sugar has dissolved completely or an instant read thermometer reads 160 degrees. Test to make sure the sugar is completely dissolved by carefully rubbing a small amount of the mixture between 2 fingers. If it feels grainy continue cooking until the sugar is fully dissolved.

Remove the bowl and place into a stand mixer or use a hand mixer and mix on medium high to high speed for 10-15 minutes until a thick and glossy meringue forms with stiff peaks.

The bowl and the meringue should be cool to the touch so if it is not, let it cool before adding the butter.

Switch to the paddle attachment if using a stand mixer and add the butter cubes, one to two tablespoons at a time, mixing well after each addition until all the butter is incorporated. *See notes or blog post for troubleshooting if your frosting is runny or curdled.

Add the salt and vanilla and mix until combined.

Add the raspberry puree and beat until combined and smooth. If the frosting curdles or separates at this point, place the bowl back over the double boiler with simmering water for about 2 minutes to melt the sides of the buttercream. Place it back into the stand mixer and beat for another couple minutes until it comes together and is light and fluffy.

Wait to make the ganache until you are ready to decorate the cake. Place the chopped chocolate in a small bowl and set aside.

Stir the cream and chocolate until it is fully melted and completely combined. Let it cool for 5 minutes but no longer as it will become too thick to pour.

Level each cake layer by using a serrated knife to make each one completely smooth on the top.

Place the first cake layer onto a cake stand or cake board using a small amount of frosting under the cake layer to keep it from sliding on the board.

Place half of the mousse over the first layer and spread it evenly over the cake and all the way to the sides.

Repeat with the next cake layer and the rest of the mousse and top it with the third cake layer.

Cover the cake with plastic wrap lightly and refrigerate the cake for at least an hour to let the mousse set up before frosting it.