Bake and cool the cake. For a tall cake like the one pictured, bake the batter in three 6 inch pans. Once cool, split them in half for a total of 6 layers.
Make the Buttercream
See recipe notes for Buttercream Recipe.
Prepare the buttercream. You'll need 4x the recipe, made with half butter and half shortening for a very white buttercream.
Assemble the Cake
Stack, fill and frost the cake, making the buttercream as smooth as possible.
If you'll be transporting the cake, then you'll need to use a cardboard cake circle and wooden dowels for support halfway up as you assemble the cake, as well as a central dowel all the way through the cake layers.
Chill the frosted cake thoroughly.
Make the Haunted House
Make your haunted house design using the sugar sheets.
After cutting out your design, keep it stored flat, inside a plastic ziplock bag to keep it from getting dry and brittle.
Decorate the Cake
Take your chilled cake out of the refrigerator.
Remove the plastic backing from your haunted house sugar decoration. Brush a little buttercream on the back side of the decoration, then position it on the front of the cake. Gently but firmly press the decoration onto the cake.
Serving and Storing
Since the cake was chilled, let it come to room temperature for several hours before serving, since room temperature cake is much better than cold cake.
Since the cake is so tall, you may want to only cut halfway down the cake, slice it all around, and then cut the bottom half into slices.
Although the sugar sheet is technically edible, it's not a very pleasant texture (like eating paper). Personally, I remove the paper before cutting and serving the cake.
Leftover cake should be stored in an airtight container for up to 3 days.