Begin at the base of the cone. Press a toothpick into the foam so that half of it is sticking out. Then, spear a donut hole onto the toothpick. (The toothpick should not go all the way through the donut.) Continue, making sure the toothpicks and donuts are tightly packed, until the first ring is complete. Then, make another ring above that, staggering the donuts so that they do not fall in a straight line. If you want to play with pattern, vary the type of donut used in each ring—or, keep it simple and leave the cake monochromatic.