Homemade Chocolate Brownie Cake with Vanilla Mascarpone Buttercream

For the brownie cake:
Preheat oven to 350°F. Grease bottom of 3 -8inch round pans with melted butter or cooking spray.

In the bowl of an electric mixer, whisk together melted butter and sugar until smooth. Add in eggs, one at a time on low speed and whisk until well combined. Using a large rubber spatula, gently stir in flour, cocoa, baking soda and salt. Spread batter into the pans and bake for 25-30 minutes until set. Remove and let cool completely before assembling the cake.

For the coconut filling:
Place the butter, walnuts and coconut in a large bowl and set aside. In a medium sauce pan, on low/medium heat, stir together the heavy cream, sugar and egg yolk until the mixture begins to thicken and coats the back of a spoon (180 degrees F.). Pour the hot custard immediately onto the walnut-coconut mixture and stir until the butter is melted. Cool completely to room temperature before topping the brownie layers.

For the vanilla mascarpone buttercream:
Place softened butter and mascarpone into the bowl of an electric stand mixer that has been fitted with the whisk attachment. Turn the mixer on a medium setting and cream until it smooth and combined, 2 – 3 minutes. Add powdered sugar, half cup at a time. Add vanilla bean and a pinch of salt and whisk until well-incorporated. If the frosting is too thick add heavy cream one tablespoon at a time until it has reached the desired consistency.

For the chocolate ganache:
Place the chocolate, corn syrup and butter in a medium bowl. Heat the cream in a small saucepan over medium heat until it just begins to boil. Remove from heat and pour over the chocolate. Let stand one minute, then stir until smooth. Cool to room temperature.

Now, assemble the cake. Remove the cooled brownie layers from the pans. Set the first cake layer on a cake plate. Top with a half of the coconut walnut filling, spreading it evenly. Top the coconut layer with ⅓ of the frosting, also spreading evenly. Repeat the process with the second brownie cake layer. Third (top) layer, is covered in frosting only, no coconut mixture. Pour the chocolate ganache on top of the cake, distribute evenly and also ice the sides of the cake while the ganache is dripping down.

Decorate with frosting if you have any remaining and chocolate sprinkles. Chill the cake for at least 2 hours before serving.