I used a classic white cake recipe and added 2 to 3 tablespoons of rainbow jimmies to the batter before dividing it into pans. The cake is made of nine 6-inch rounds.
I made a base for the cake so that it would appear to taper in by hot gluing together 3 cardboard rounds that I had cut about .25 an inch off all around. I cut a hole through the center and glued a disposable chopstick sticking straight up. I had also made sure I cut a hole through the center of the cake board that the bottom 6-inch cake round was sitting on so that I would be able to insert the chopstick up the center of the cake, giving it stability. I also inserted a second chopstick going down into the center from the top too.
The hardest part was actually getting the cake covered in fondant. I tried about 5 different times. I rolled out a big circle of fondant to drape over and tried to smooth out the folds but it didn't work out because there were was too many folds to smooth down. The only way I was successful in getting it covered was to roll out a long piece of fondant on a piece of parchment paper and wrap it around the sides. I could have really used a second pair of hands for this. Then I rolled another smaller circle to put on top and join the seams as best as I could.