Ingredients

2 ½ cups all-purpose flour

2 cups granulated sugar

1 tablespoon baking powder

1 teaspoon kosher salt

1 cup (2 sticks) unsalted butter, softened

2 large eggs + 2 egg whites

1 ½ cups buttermilk

½ cup vegetable oil

1 tablespoon vanilla extract

½ cup rainbow sprinkles, plus more to decorate cake

½ cup (1 stick) unsalted butter, softened (for frosting)

2 cups powdered sugar, sifted if lumpy

2 tablespoons milk of choice

1 tablespoon vanilla essence (extract or paste)

Instructions

Step 1: Preheat the oven to 350°F. Coat a 9×13-inch baking pan with non-stick spray, then line it with parchment paper leaving a little overhang on the sides. Set aside.

Step 2: In a large mixing bowl or stand mixer, whisk together the flour, sugar, baking powder, and salt until well combined.

Step 3: Add the softened butter and beat on medium speed until the mixture looks crumbly and sandy, about 2-3 minutes. This reverse creaming method will create a texture similar to cake batter.

Step 4: Add the eggs, egg whites, buttermilk, vegetable oil, and vanilla extract. Beat until the batter is thick and smooth, about 2-3 minutes, stopping to scrape down the sides as needed.

Step 5: Fold in ½ cup of rainbow sprinkles gently with a rubber spatula. Pour the batter into the prepared pan and smooth the top using an offset spatula.

Step 6: Bake for 35-40 minutes at 350°F, or until a toothpick inserted in the center comes out clean.

Step 7: While the cake bakes, prepare the frosting. Beat the softened butter until creamy, about 1-2 minutes.

Step 8: Add the powdered sugar and continue beating until smooth and well combined, 1-2 minutes.

Step 9: Add the milk and vanilla essence, beating until the frosting is silky smooth.

Step 10: When the cake is done, let it cool in the pan for 15 minutes. Then remove the cake using the parchment overhang and transfer it to a cooling rack to cool completely.

Step 11: Once fully cooled, spread the frosting evenly across the top and decorate with additional rainbow sprinkles.

Step 12: Slice into 12 wedges and serve. Enjoy your colorful, fluffy funfetti sheet cake!

Tips & Variations

For a dairy-free version, substitute the buttermilk with a plant-based milk mixed with 1 tablespoon of lemon juice and use dairy-free butter and milk for the frosting.

Use gel food coloring to tint the frosting for an extra pop of color.

Mix the sprinkles in gently to avoid melting their color into the batter.

Try adding a teaspoon of almond extract along with vanilla for a different flavor profile.

Storage

Store the frosted cake covered at room temperature for up to 2 days or in the refrigerator for up to 5 days. If refrigerated, let the cake come to room temperature before serving for best texture. Leftovers can be wrapped tightly and frozen for up to 2 months; thaw overnight in the fridge and frost as desired.

FAQs

Can I use a different pan size for this recipe?

This recipe is designed for a 9×13-inch pan. Using a different size may affect baking time and thickness, so adjust accordingly and test doneness with a toothpick.