Instructions

1. 1

   Preheat the oven to 350°F. Grease and line two 9-inch cake pans with parchment paper so the layers release cleanly after baking.

2. 2

   In a large bowl, whisk together the flour, cocoa powder, sugar, baking soda, baking powder, and salt until the cocoa is evenly distributed with no visible lumps.

3. 3

   Add the eggs, buttermilk, oil, and vanilla. Mix until the batter looks thick and glossy. Slowly pour in the hot coffee and stir gently. The batter will become very thin, which helps create a soft chocolate mousse cake texture once baked.

4. 4

   Divide the batter between the pans and bake for 24 to 28 minutes. The tops should spring back lightly when touched, and a toothpick should come out with only a few moist crumbs attached.

5. 5

   Let the cakes cool in the pans for 10 minutes before turning them onto a wire rack. Cool completely before adding the filling.

6. 6

   For the white chocolate filling, heat the heavy cream in a saucepan just until steaming. Pour it over the chopped white chocolate and let it sit for 2 minutes. Stir until smooth and glossy.

7. 7

   Beat the cream cheese and vanilla until smooth, then slowly add the white chocolate mixture. Continue mixing until the filling looks silky and thick enough to spread without running.

8. 8

   To make the frosting, beat the butter until pale and fluffy. Add the powdered sugar and cocoa powder in batches, alternating with the cream. Mix until smooth and spreadable with a deep chocolate color.

9. 9

   Place one cake layer on a serving plate. Spread the white chocolate filling all the way to the edges in an even layer. Top with the second cake layer and gently press down until level.

10. 10

    Frost the top and sides with the chocolate frosting. A common tip is to chill the cake for 20 minutes before the final frosting pass so the crumbs stay contained and the finish looks smoother.