Unsalted butter, for pans
Unsweetened Dutch-process cocoa powder, for pans
3 batches Devil’s Food Cake Batter
1 package (10.58 ounces) soft chocolate torrone or nougat, cut into 2- to 2 1/2-inch blocks
1 thick block milk chocolate, for shaving
Haunted-House Chocolate Cookies
Candy Cats, optional
Preheat oven to 350. Butter three 11-by-2-inch round cake pans and three 9-by-2-inch round cake pans. Line bottoms with parchment, then butter parchment. Dust pans with cocoa powder, and tap out excess.
Pour 5 cups devil’s food cake batter into each 11-inch pan and 3 cups batter into each 9-inch pan. Bake, rotating pans halfway, until testers inserted in centers come out clean, 40 to 45 minutes. Let cool in pans on wire racks. Invert cakes. Remove parchment. Trim tops of each cake to create a flat surface. Reserve trimmings for another use.
To assemble the cake: Secure one 11-inch cake layer to corresponding-size round foam board with a dab of chocolate buttercream. Spread 2 cups buttercream on top. Stack another 11-inch cake on top of frosting, and frost as before. Top with remaining 11-inch cake. Spread 1 cup frosting over top and sides of tier, scraping lightly to create a crumb coat, and refrigerate until frosting is firm, about 30 minutes. Spread 2 cups frosting over entire tier until smooth. Repeat with 9-inch cake layers, using 1 cup frosting between layers, 1/2 cup for crumb coat, and 1 cup for the final coat. Trim 5 dowels to height of 9-inch tier and 6 to height of 11-inch tier. Insert dowels in corresponding tiers in a circle 2 1/2 inches from the edge of cake.
Center 9-inch tier over 11-inch tier, pressing gently to secure. Fill a pastry bag fitted with a 1/2-inch round tip with remaining buttercream. Pipe pearls around bottoms of tiers.
Cut toothpicks in half. Insert into torrone blocks, and push blocks into cake to create steps, starting from top of 9-inch tier and curving to bottom of 11-inch tier. Using a vegetable peeler, shave milk chocolate, and sprinkle over tops of both tiers.
Carefully transfer house to top of cake. Press cookie doors into cake in front of house. Decorate cake with cookie tree, tombstones, and candy cats if desired. Press caretaker cutout onto top of cake, behind house door. Arrange a flashlight behind cake to shine through door and windows. Cake will keep, refrigerated, up to 3 days.