Rainbow Cake Recipe

Prepare

Preheat the oven to 350°F (175°C). Grease and line six 8-inch round cake pans with parchment paper, or if you have fewer pans, plan to bake in batches. If using fewer pans, divide batter accordingly.

Dry ingredients

In a large bowl, whisk together 3 cups all-purpose flour, 2 cups granulated sugar, 3 tsp baking powder, and 1 tsp salt until evenly combined.

Cream butter and wet

In a stand mixer fitted with the paddle (or using a hand mixer), cream 1 cup softened unsalted butter on medium speed for 1–2 minutes until smooth. Add the 4 eggs one at a time, mixing 20–30 seconds after each addition. Mix in 2 tsp vanilla extract and 2 tbsp vegetable oil until incorporated.

Combine wet and dry

With mixer on low, add one-third of the dry mixture, then half of 1 cup milk, then another third of the dry, then the remaining milk, then the last third of the dry. Mix just until combined after each addition (do not overmix). Fold in 1 cup Greek yogurt until batter is smooth and medium-thick.

Divide and color

Divide the batter evenly into six bowls (about 1 1/4 to 1 1/2 cups per bowl, depending on exact yield). Using gel food coloring (stronger than liquid), tint each bowl a different color: red, orange, yellow, green, blue, purple. Start with a small amount and add more until vivid colors are achieved. Stir each until evenly colored.

Bake

Spoon each colored batter into prepared pans, smoothing the tops. Bake for 10–14 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs and the tops spring back when touched. If baking in batches with fewer pans, monitor closely—thinner spreads may bake faster.

Cool

Remove cakes from oven and let cool in pans for 5–10 minutes. Run a knife around edges, invert onto wire racks, peel off parchment, and let layers cool completely (at least 1 hour) before assembling.

While cakes cool, make syrup: combine 1 cup water and 1 cup granulated sugar in a small saucepan. Bring to a simmer and stir until sugar dissolves. Remove from heat and stir in 1 tsp vanilla. Let cool. Brush a light coat on each cake layer before frosting to keep them moist.

Beat butter and cream cheese

In a large bowl or stand mixer, beat 1 cup softened unsalted butter and 8 oz softened cream cheese on medium speed until smooth and homogenous, about 2–3 minutes.

Add sugar and flavor

With mixer on low, gradually add 6 cups confectioners' sugar, 1 cup at a time, to prevent a sugar cloud. After incorporated, add 2 tsp vanilla extract and a pinch of salt.

Adjust texture

Raise mixer speed to medium-high and beat for 1–2 minutes until light and fluffy. If frosting is too thick, add up to 2 tbsp heavy cream or milk, 1 tsp at a time, until spreadable. If too thin, add a little more powdered sugar.

Level layers

If layer tops dome, level them with a serrated knife or cake leveler so each layer is flat for stable stacking.

Stack the cake

Place the purple layer (or your chosen bottom color) on a cake board or serving plate. Brush lightly with simple syrup if using. Spread an even layer (about 1/2 to 3/4 cup) of cream cheese buttercream over the layer. Repeat with blue, green, yellow, orange, and finally red on top, brushing each with syrup and adding frosting between layers for even coverage.

Crumb coat

Apply a thin crumb coat of frosting over the entire stacked cake to trap crumbs. Chill the cake in the refrigerator for 20–30 minutes to set the crumb coat.

Final coat and decorate

Apply a final thicker coat of frosting, smoothing with an offset spatula or bench scraper. Add sprinkles around the top edge or sides as desired. Use extra gel to touch up any areas or to pipe small accents if desired. Chill briefly to firm frosting before serving, but bring to room temperature 20–30 minutes before slicing for best texture.

Slice and serve

Use a sharp knife wiped clean between cuts to slice the cake, revealing rainbow layers. Store leftover cake covered in the refrigerator for up to 4 days.