Creating a large layer cake is a labor of love, but you can do a few things to make it less labor and more love. Above all, make sure you have everything ready to go before you begin, and make sure you leave yourself enough time. There is nothing more frustrating than wrestling with unruly frosting and watching to clock tick down ominously to party time. I did the butterfly cake over several days, and, for the most part, it worked out beautifully.
Below is my cake mise en place. You can see, clockwise from bottom left, the quarter-sheet chocolate cake, already layered and on the turntable, extra cardboard cake sheets, chocolate ganache, sweetened whipped cream, raspberries, and raspberry simple syrup in a squirt bottle. (The squirt bottle is a great secret: instead of applying simple syrup with a pastry brush, which can take FOREVER, put it in a clean bottle and spritz your layers with the syrup. Much faster, and I think the coverage is more even).
Lather, rinse and repeat. Four layers of cake and three layers of filling later, I had created a monster. It was over 5 inches high, and incredibly heavy. I wish I'd thought to stick it on the scale! Maybe ignorance is bliss, though...
I did all the layering in one evening, and then wrapped my baby tightly in saran and put it in the refrigerator overnight. The fridge isn't ideal, because it can make the cake dry (and can transmit funny smells), but what else is a busy working girl to do? The next evening, when I was ready to get serious and finish the cake, I put it in the freezer for about 30 minutes to really firm up. While it was chilling, I freehanded a butterfly pattern on a large sheet of paper, and cut it out. When the cake came out of the freezer, I placed the pattern on the cake and cut around it with a very sharp knife. Even though the cake was large and in charge, the pattern wasn't much of a problem, probably because it wasn't very detailed. Whew!
worst best part of the sculpted cake idea? Cake scraps!
I gave my cake a quick crumb layer with the chocolate ganache and stuck it back in the freezer for another half-hour. I should mention at this point that I made the freakiest chocolate ganache ever. I made it one evening, and it was fine. Used it to frost between the cake layers, still fine. Wake up the next morning and it has completely broken. Broken, like it looked like chocolate tapioca. Perplexing and nasty. I don't know what happened, or what got into it, but I really didn't want to buy 5 more pounds of chocolate and start all over. So I heated it over a bain marie, added a bit more warm cream, and whisked the life out of it. Once it set it behaved better, but I don't think it ever truly recovered. So I had some difficulty smoothing out the ganache, but considering what I had to work with, I guess it's the best I could hope for!
Anyhow--popped it out of the freezer, and frosted it smooth with chocolate ganache. The freezer step isn't necessary, but it is useful if you need to firm up your layers (so the cake doesn't fall apart as you're frosting) and it also helps the frosting to "set" quickly. If you're using a really loose buttercream or ganache, it can be useful to have a very cold cake, so that the frosting will firm up immediately on contact, and you don't have to worry about it sliding all over. So here is the finished cake. Notice how the cardboard underneath is all dirty? I actually cut out a cake board in the shape of a butterfly, and the cake is sitting right on top of that board--so I can easily lift it off the dirty board and put it on a clean one.
All that's left is to decorate! I used dark and white chocolate circle cutouts to create my pop-art butterfly. The chocolate was melted (and in the case of the white chocolate, tinted different shades of pink) and poured in a thin layer over foil. Once it was set but not brittle, I used fondant cutters to cut out circles of different sizes, let it harden completely, then popped the circles out and stored them in tupperware. I did this about a week in advance. The circles were attached using a small dab of melted chocolate.
I also used sparkling pink sugar on some of the dark chocolate circles. I was excited about the idea, but it didn't "pop" as much as I was hoping it would.
My antennae! I piped molding chocolate in antenna shapes and sprinkled the ends with pink sugar, then let it harden in the freezer. I wasn't sure they would stick in the cake, but the ganache hardened quite a bit, and it was super easy to skewer the cake. I painted melted chocolate around the insertion points just to be sure they wouldn't fall. Finished with some spiky balls of pink buttercream around the butterfly, wrote on the cakeboard, and voila! The butterfly, she is ready to eat.