FOR THE CAKES:
Cooking spray
2 boxes white cake mix (plus ingredients called for on box)
1 (3.4-o.) box orange Jell-O
FOR THE FROSTING:
4 c. (8 sticks) butter, softened
13 c. powdered sugar
1/2 c. whole milk, plus more if needed
Orange food coloring
Step 1
Make cake: Preheat oven to 350° and line three 8" cake pans with parchment paper. Grease with cooking spray. In a large bowl, prepare cake mixes according to package instructions. Gently fold in jello. Divide among pans and bake until a toothpick inserted into middle comes out clean, about 25 minutes. Let cool completely.
Step 2
Make frosting: In another large bowl using a hand mixer, beat butter with half the powdered sugar until smooth. Add remaining powdered sugar and ½ cup milk and beat until fluffy. If mixture is too stiff, add more milk.
Step 3
Level tops of each cake with a serrated knife to create even layers. Place down one cake and top with a heaping cup of frosting, then top with second cake and repeat with third layer.
Step 4
Using about 1 1/2 cups of frosting, smooth a crumb coat around outside of the cake. Transfer cake to refrigerator until frosting is hardened, 30 minutes to 1 hour.
Step 5
Meanwhile, divide frosting. Fit 4 pastry bags with ½-inch round tips and fit another pastry bag with a ½-inch star tip, set aside.
Step 6
Fill 3 bowls with 1 ¾ cups each of frosting. Scrape remaining frosting into one of the prepared round tip pastry bags. Using the food coloring, dye one bowl of frosting light orange, another medium orange, and the final a bright orange. Scrape each of the orange mixtures into one of the prepared pastry bags with the round tips.
Step 7
Remove cake from the refrigerator and pipe the bright orange frosting in 4 circles around the cake. Followed by 4 circles of the medium orange, 4 circles of the light orange, and the white until you hit the top. Pipe the remaining white frosting around the top of the cake.
Step 8
Using a metal bench scraper or offset spatula, smooth the outside and top of the cake, keeping the colored layers more or less in the same place.
Step 9
Remove the remaining frosting from the piping bags. Combine the leftover orange frosting in one bowl and place the white frosting in a separate bowl. Fill one side of the prepared pastry bag with the star tip with the orange and the other side with the white. Pipe stars around the perimeter of the cake. Refrigerate until ready to serve.