1Heat the oven to 350°F. Butter and flour two 9-inch round cake pans. In a bowl, combine the coffee and cocoa powder and whisk until smooth. Add 1 cup cold water and whisk until combined. In a separate bowl, sift together the flour, baking soda, salt, and baking powder. Set aside.
2Using an electric mixer, beat the butter and sugar on medium speed until light and fluffy. Continue beating at medium speed while slowly adding the eggs and vanilla. Scrape down the sides of the bowl as necessary. Add the dry ingredients to the butter mixture alternately with the cocoa mixture until well combined. Pour into the prepared cake pans and bake until a toothpick inserted into the center of the cake comes out clean, about 45 minutes.
3Allow to cool 10 minutes in the cake pans, then turn out onto wire racks to cool completely.
For the mascarpone cream:
1Whisk the mascarpone, cream, and sugar until stiff peaks form. Gently fold in the cookie bits using a rubber spatula. Set aside.
For the chocolate buttercream:
1Melt the chocolate in a double boiler over low heat; set aside to cool. Combine the butter, cocoa powder, and powdered sugar and beat until smooth. Scrape down the sides of the bowl, and add the vanilla and cooled chocolate. Beat until well incorporated. Set aside at room temperature.
1Trim both of the cake layers with a serrated knife until flat and uniform. Place one cake layer on a cake stand or platter, trimmed side up. Using a spatula, spread all of the mascarpone cream on top of the cake layer. Place the second layer directly on top, trimmed side down.
2Spread the chocolate buttercream over the top and sides of the cake, swirling it decoratively. Using your hands, lightly press cookie crumbs onto the bottom inch of the sides of the cake, creating a cookie crumb border.
This recipe, while from a trusted source, may not have been tested by the CHOW food team.