Rainbow Cake

Make Rainbow Cake with vibrant layers and silky buttercream, perfect for celebrations and everyday joy.

Ingredients

• 5 cups all-purpose flour (600g)
• 3 cups granulated sugar (600g)
• 1 tablespoon baking powder
• ½ teaspoon baking soda
• 1 teaspoon salt
• 6 large eggs (room temperature)
• 1½ cups vegetable oil (360ml)
• 1½ cups whole milk (360ml)
• 1 tablespoon vanilla extract
• Food coloring (red, yellow, blue, green)
• 2½ cups unsalted butter (softened (565g))
• ½ teaspoon salt
• 10 cups confectioners' sugar (1200g)
• ½ cup cream (room temperature (120ml))
• 2 teaspoons vanilla extract

Instructions

Step 1: Mix and prepare the rainbow cake batter

Preheat the oven to 350°F, grease two or three 8-inch round cake pans with baking spray or softened butter and line the bottoms with parchment paper. In a large mixing bowl whisk together the flour, granulated sugar, baking powder, baking soda, and salt until evenly combined and aerated; in a separate bowl whisk the eggs, vegetable oil, whole milk, and vanilla until smooth, then fold the wet ingredients into the dry until a cohesive, ribbon-thick batter forms. Divide the batter evenly among six small mixing bowls and tint each bowl with food coloring to yield vibrant red, orange, yellow, green, blue, and purple batters; transfer a single colored batter to a prepared cake pan and cover the remaining bowls lightly with plastic wrap and chill briefly to slow the leavening reaction while you bake in batches. Bake each filled pan for about 20 minutes or until a toothpick comes out clean, cool in the pan for 10 minutes then unmold onto a wire rack to finish cooling; wash, re-line, and repeat until all six layers are baked and fully cool.

Step 2: Whip the buttercream to a silky, stable texture

In the bowl of a stand mixer fitted with the whisk attachment, beat the softened unsalted butter with the pinch of salt on medium speed until very pale and airy (about 5 minutes), then reduce speed to low and add the confectioners’ sugar a cup at a time, incorporating a tablespoon of cream as needed to maintain a smooth, spreadable consistency. Pause occasionally to scrape the bowl, then beat in the vanilla and increase speed to medium-low for a final minute of whipping until the buttercream is light, glossy, and pipeable—add a touch more cream only if the mixture feels grainy when rubbed between your fingers.

Step 3: Assemble, chill, and plate the rainbow cake

Remove parchment from each cooled layer and stack starting with purple at the bottom, spreading roughly ½ cup of frosting between each layer in the order purple, blue, green, yellow, orange, then red on top, using an offset spatula to keep edges neat; once stacked, apply a thin crumb coat then a final smooth outer layer of buttercream, finish with a decorative swirl at the base and a scattering of colorful sprinkles if desired. Chill the completed cake for at least one hour to set the frosting before slicing; store any leftovers covered at room temperature for up to three days.

Notes

• Use gel food coloring to get bright colors without thinning the batter.
• Weigh flour for consistent results; spoon into the cup and level.
• Cool layers completely before stacking to avoid a sliding cake.
• Sift confectioners' sugar into the buttercream to keep it silky.
• If you need thinner frosting, add cream 1 teaspoon at a time until desired consistency.