Makes: 12 servings
1 white cake mix
1 dark chocolate fudge cake mix
2 ounces sweet baking chocolate, melted and cooled
4 cans milk chocolate frosting
1⁄2 cup unsweetened cocoa powder, sifted
4 tablespoons cooled espresso
Prepare each cake mix individually according to package directions. Stir the cooled melted chocolate into the yellow cake batter. Spray four 9×11⁄2-inch nonstick pans with cooking spray. Divide light chocolate batter between two pans. Divide dark chocolate fudge batter between the other two pans. Bake according to package directions.
Let cakes cool in wire racks for 15 minutes. Remove from pans and cool completely. Set aside one of the light layers for another use.
With a long serrated knife, trim the tops from the light layer and one of the dark layers to make a flat surface.
Place a dark chocolate layer on a serving platter. Frost top generously with milk chocolate frosting. Lay a light chocolate layer on top. Frost top generously with milk chocolate frosting. Lay the second dark chocolate layer (untrimmed) on top. Frost the sides and top of the cake with milk chocolate frosting, reserving ½ cup.
In a small bowl stir together the remaining milk chocolate frosting, cocoa powder, and espresso. Swirl the darker frosting into the milk chocolate frosting on the top of the cake.