Basic supplies, minus the sprinkles and duplicate boxes of frosting and cake mix.
Preheat oven to temperature give on cake box, then make both boxes.
Divide cake batter evenly into 6 bowls. I used about 1.5-2 cups of batter per bowl.
Add food coloring to bowls. Make red, orange (14 drops yellow, 7 drops red), yellow, green, blue, and purple (14 drops red, 7 drops blue). I did about 20 drops to make each color.
Tip: to mix food coloring more easily, transfer the small bowl into a larger bowl. While that layer bakes, wash out the bowl and do the next color.
Spread the first color evenly on to the pan. Line the pan with parchment paper and have it hang over the edges for easy removal.
Tip: use chip clips to hold the parchment paper into place. It makes this step much easier. Just remember to take them off before baking!
Bake for 10 minutes.
Let cool in pan for 10 minutes, then move to cooling rack. Don't remove the parchment paper.
Repeat for the rest of the layers.
While those finish cooling, make the frosting. I just follow the recipe on the box.
Place the red layer back in the pan, keeping the parchment paper on.
Carefully place the orange layer on top of the red one and peel the parchment paper off.
Repeat for the rest of the layers, but don't frost the top of the purple one.
Cover with parchment paper.
Wrap with foil and place in freezer with heavy items on top of it. Let sit for several hours or overnight.
Use a biscuit cutter, a cup, or the sprinkles jar (like I'm using) to cut out the cylinders. If you use the sprinkles jar, cut around it with a knife.
Frost the tops.
Then top with sprinkles and candles if you want!
Not sure what to do with the scraps? Turn them into cakeballs!