Ingredients

• Unsalted butter, for the pans
• 2 1/4 cups granulated sugar
• 1 cup vegetable oil
• 4 large eggs
• 2 teaspoons vanilla extract
• 3 3/4 cups all-purpose flour
• 3/4 teaspoon baking soda
• 1/2 teaspoon salt
• 1 1/2 cups buttermilk
• Gel food coloring
• 8 sticks unsalted butter, cut into pieces, at room temperature
• Pinch of salt
• 10 cups confectioners' sugar, sifted
• 2 tablespoons vanilla extract
• 6 to 8 tablespoons milk
• Assorted toppings (see below instructions)

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Instructions

1. Make the cake: Position a rack in the lower third of the oven and preheat to 350 degrees F. Butter four 9-inch-round pans and line the bottoms with parchment paper. Combine the granulated sugar and vegetable oil in a large bowl and beat with a mixer on medium-high speed until thick and creamy, about 3 minutes. Beat in the eggs, one at a time, then add the vanilla and beat on high speed until the batter is light and fluffy, about 2 minutes.
2. Sift the flour, baking soda and salt into a medium bowl. With the mixer on low speed, beat the flour mixture into the sugar mixture in 3 additions, alternating with the buttermilk, beginning and ending with the flour mixture, until the batter is smooth, about 2 minutes. Tint with gel food coloring (see below).
3. Divide the batter among the prepared pans and bake, 2 pans at a time, until a toothpick inserted into the centers comes out clean, about 15 minutes. Let cool 15 minutes in the pans, then invert onto racks to cool completely.
4. Make the frosting: Beat the butter and salt in a large bowl with a mixer on medium speed until smooth and fluffy, about 2 minutes. Gradually beat in the confectioners' sugar until smooth. Add the vanilla, increase the mixer speed to medium high and beat until thick, 2 more minutes. Beat in the milk, a little at a time, until the frosting is spreadable.
5. Assemble the cake: Spread about 1 1/2 cups frosting between the cake layers, then cover the outside of the cake with the remaining frosting and coat with toppings (see below).
6. How to Color the Batter:
7. Use gel food coloring for cakes: You don't need to add as much, and the colors are brighter.
8. Solid: Tint the batter 1 color; divide among 4 pans.
9. Striped: Divide the batter between 2 bowls; tint each one a different color. Divide each color between 2 pans.
10. Ombre: Divide the batter among 4 bowls; tint in varying shades of the same color. Pour into 4 pans.
11. Rainbow: Divide the batter among 4 bowls; tint each one a different color. Pour into 4 pans.
12. The Toppings:
13. Mini Marshmallows: You'll need about one 10 1/2-ounce bag. For a multicolored look, use fruit-flavored mini marshmallows.
14. Chocolate Rocks: You'll need about 3 cups. Find them at specialty candy stores, or order online.
15. Ombre Coconut: Divide one 7-ounce bag coconut among 3 resealable plastic bags. Add an increasing number of drops of the same food coloring to each bag and shake.
16. Nonpareils: Use rainbow or single-color nonpareils; you'll need about 3/4 cup. Set your cake on a cake plate in the sink or on a large rimmed baking sheet to catch loose nonpareils.
17. Photograph by Justin Walker