Made with cotton candy vapor and a cardboard-tube neck, this cake is modeled after a real piece of lab equipment: a Florence flask. Experiment with serving it at the Mad Scientist's Blast Party.
Mix 10 drops of neon blue food coloring into 1 1/2 cups of white frosting. Spoon 1/4 cup of the blue frosting, all of the chocolate frosting, and 2 tablespoons of the white frosting into separate ziplock bags.
If needed, trim the flat sides of the cakes with a long serrated knife to make them level. Place one cake, round side down, on a serving platter, and spread 1/2 cup of white frosting on the top. Place the second cake on top of the first, rounded side up, so the scalloped edges on the cakes line up.
Wrap the cardboard tube with aluminum foil and secure the foil with tape. Insert the tube into the center of the cake.
Spread the remaining white frosting onto the top half of the cake and the tube, using a generous amount at the intersection of the tube and the cake so that it makes a nice curve. Use a small offset spatula to lightly smooth the sides.
Spread the remaining blue frosting around the bottom half of the cake as shown.
Snip small corners from the frosting-filled bags. Pipe on horizontal measurement lines, numbers, and bubbles, as shown. Use the remaining white frosting to pipe a lip around the opening of the tube.
Tuck a large tuft of cotton candy into the top of the tube. Use a wooden skewer or toothpick to tease it out. Serves 24.
Extra Credit Lab: This cool substitution will wow young scientists. Instead of the cardboard tube, use PVC pipe with an end cap at the bottom. Add dry ice and warm water to the pipe, and real vapor will cascade dramatically from the top of the flask.