Place one of the white layers on a cake stand, center. Center a 3-inch round cutter over the cake layer and press in slightly to make an indentation. Using a small knife held at a 45 degree angle, slice into the cake, aiming for the center. Follow the indentation around the cake and remove the cake cone. Repeat with the pink cake layer. Place the pink cake cone into the hole of the white cake layer.
Use a 4-inch round cutter to make indentations in the remaining 2 white cake layers. Use the back of a spoon to dig a ¼-inch deep channel in one of the cakes, and a 1/2-inch deep channel in the other.
Crumble the rest of the pink cake into a small bowl. Add 2 tablespoons of the buttercream and a little black gel food coloring and combine with a fork until uniformly black. Add additional buttercream and food coloring if needed.
Roll the black cake mixture into logs thick enough to fill the cavity in the cake layer. Lay them into the cake layer with the deeper channel and connect them to fit evenly.
Crumble all of the white cake scraps and combine with 1 tablespoon of the buttercream and a little white gel food coloring. Roll the white cake mixture into logs and then flatten with your hands to about ¼ inch thick. Place on top of the black logs, covering it completely.
Spread a thin layer of buttercream around the edge of the cake layer on the cake stand, being careful to avoid the pink cake cone.
Set the layer with the black logs on top and cover the edge with buttercream. Turn the remaining cake layer over and place on top, making sure the black log fits into the carved-out top layer.
Cover the cake with a thin crumb coat and chill in the fridge for 1 hour.
Fill a pastry bag fitted with a small star tip with the remaining buttercream. Pipe small bursts of frosting over the surface of the cake, making sure they are fairly uniform in size.
To make a bunny tail, pipe out a big ball of frosting at the back of the cake. Cover with small bursts of buttercream.
To make the bunny ears, trace an outline of bunny ears onto a sheet of paper and then place that paper under parchment paper on a baking sheet. Melt the white candy melts in a zipped plastic bag in the microwave in 30 second bursts. Massage the bag to fully melt the candy.
Cut a small hole in the corner of the bag and pipe out the inside of the ears onto the parchment paper. Use a small spatula to smooth it out, if necessary. Repeat with the pink candy melts. Chill in the fridge for 30 minutes or in the freezer for two minutes.
Chill the cake until ready to serve and insert the bunny ears into the cake just before serving.