1 lb (454g) unsalted butter, cubed and at room temp.
For the chocolate ganache:
100g dark chocolate
100g heavy cream
For filling and garnishing:
Coarsely chopped chocolate chip cookies and oreos
Chocolate covered espresso beans
For the chocolate cake, whisk together the dark chocolate and boiling water until the chocolate is completely melted (set aside to cool). Whisk the egg on high until light and fluffy, and then whisk in the vegetable oil. Whisk in the rest of the chocolate cake ingredients (including the water/chocolate mixture) until just combined, and pour into two greased and lined 6″ cake pans. Bake at 350F/175C for 20-25 minutes, or until a toothpick inserted in the center comes out clean.
For the vanilla bean cake, melt the butter and whisk in the milk. Heat the milk/butter mixture in the microwave for a few seconds if the two start to separate (set aside to cool). In a bowl, whisk together the eggs, sugar, vanilla extract, baking powder, and flour. Cut apart your vanilla bean and scrape the contents into the bowl. Whisk in the butter/milk mixture until just combined. Pour your batter into two greased and lined 6″ cake pans and bake at 350F/175C for 20-25 minutes, or until toothpicks inserted in the center come out clean.
To make the espresso buttercream, combine the water and granulated sugar in a small saucepan and the mixture reaches 230F/110C. While the sugar and water cook, whisk your egg whites until they hold stiff peaks in a stand mixer. Slowly pour the hot syrup into your egg whites, whisking continually on low-medium speed. Increase the speed on your mixer to high and continue whisking until the mixture has cooled to room temperature. In a small bowl, stir together your espresso powder and water, and add that as you add your cubes of butter. Whisk until the mixture becomes a smooth frosting.
To assemble your cake, alternate layers of chocolate and vanilla bean cake with a healthy helping of espresso frosting (1/2″-1″ between each layer of cake). Extra points if you add coarsely chopped chocolate chip cookies and oreos between each layer. Crumb coat your cake and refrigerate for 15-20 minutes to keep those dark crumbs out of your outer layer of frosting. Finish frosting the top and sides of your cake as desired, and set aside to firm up in the refrigerator for another 20-30 minutes.
To make the chocolate ganache, heat your heavy cream and dark chocolate in the microwave, stirring between each heating, until the chocolate is melted and the ganache is smooth. Set aside until the ganache is no longer warm but still easily spreadable.
Remove your cake from the refrigerator and cover the top with the chocolate ganache, allowing it to drip over the sides. Garnish with any leftover espresso frosting and chocolate covered espresso beans.