A stunning six-layer rainbow cake with buttercream frosting between each colorful layer, perfect for birthdays, holidays, and special celebrations. Moist, flavorful, and surprisingly easy to make despite its impressive appearance.
gel food coloring (violet, blue, green, yellow, orange, red)to taste
unsalted butter2½ cups
powdered sugar9 cups
heavy creamto taste
vanilla extract2 tsp
Steps
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1
Preheat the oven to 350°F.
2
In a large bowl, combine all dry ingredients—flour, salt, baking soda, baking powder, and granulated sugar—and whisk together until well mixed.
3
In a separate large bowl, crack six room-temperature eggs and check for shells. Add whole milk, vegetable oil, and vanilla extract, then whisk until combined.
4
Prepare six bowls and gather your food coloring. Pour the wet ingredients into the dry mixture and gently fold together until the flour just disappears, being careful not to overmix the batter.
5
Divide the batter equally among the six bowls (about 360g each). Add violet, blue, green, yellow, orange, and red gel food coloring (approximately 2 drops per bowl), stirring until evenly colored. The colors should be slightly deeper than desired, as they will lighten during baking.
6
Prepare six 8-inch cake pans by spraying with baking spray or butter and lining with parchment paper. Divide the colored batters evenly among the pans.
7
Place the pans in the 350°F oven and bake for about 20 minutes, until the centers are set. Test with a toothpick or check for springiness.
8
Make the vanilla buttercream: Using an electric mixer, cream together 2.5 cups of room-temperature unsalted butter and a heaping quarter teaspoon of salt until pale and fluffy.
9
Beat on medium speed for 5 minutes to incorporate air. Gradually add 9 to 10 cups of powdered sugar on low speed, alternating with small amounts of heavy cream until you achieve the desired sweetness and consistency.
10
Stir in 2 teaspoons of vanilla extract and taste to adjust the flavor. Keep the buttercream in the mixer and give it a brief 30-second whip before decorating to restore the creamy consistency.
11
Once the cakes are completely cool, place a small dollop of buttercream on the cake plate and center the purple layer. Spread about half a cup of buttercream between each layer, smoothing it into a thin, even layer, and stack the blue, green, yellow, orange, and red layers in order.
12
Spread buttercream over the entire exterior of the cake, filling any gaps between layers. Use your fingers to brace the top for support while frosting. Use a bench scraper to smooth the outside, turning the cake as you go.
13
Prepare a small batch of extra buttercream for decoration. Using a piping bag with a closed star tip, create decorative spirals around the top and bottom edges of the cake. Sprinkle colorful sprinkles over the top and bottom.
14
Refrigerate the finished cake briefly to set before slicing and serving.
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