Preheat your oven to 325F (160C). (Use an oven thermometer for best results.)
Line the bottom of three 8" round pans with parchment paper, and then spray with non-stick cooking spray.
Combine cake mixes with eggs, oil (or applesauce) and water. Mix just until no lumps remain.
Pour the batter evenly divided into the three pans.
Bake for 24-28 minutes, or just until a toothpick inserted comes out clean.
Cool for about 10 minutes before removing the cakes from the pans. Then cool completely before frosting.
Layer and frost the cake. (This is a helpful video on how to frost a layer cake.) Add sprinkles, slice, and enjoy!
The cake will store well (frosted or unfrosted) refrigerated or frozen.