Food Recipe

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Rainbow Layer Cake with Dreamy Buttercream Frosting

There’s something undeniably magical about a rainbow. It’s a fleeting promise of beauty after a storm, a vibrant arc painted across the sky that always elicits a sense of wonder. For me, that wonder is amplified tenfold when that same spectrum of color is found within the comforting embrace of a cake. I remember as a child, receiving a homemade rainbow cake for my half-birthday—a concept my younger self found delightfully absurd and utterly perfect. The sheer joy of slicing into that cake and revealing its hidden, technicolor strata was a memory etched in pure, unadulterated delight. It wasn’t just a dessert; it was an edible celebration, a whimsical creation that captured the effervescence of childhood and the simple pleasure of something truly special.

Recipe Overview

Prep Time: 20 minutes
Cook Time: 18 to 20 minutes per batch of layers
Total Time: Around 1 hour 30 minutes (plus cooling time)
Servings: 10
Yield: 1 six-layer cake
Dietary Type: Vegetarian

Ingredients

For the Cake Layers:

2 (18 ounce) boxes Betty Crocker Supermoist White Cake Mix
2 cups water
1 cup vegetable oil
6 large eggs
2 bottles Betty Crocker Gel Food Coloring (you’ll need red, yellow, blue, and green, or use the red and blue to create orange and purple)

For the Buttercream Frosting:

1 cup shortening
1 cup butter, softened
2 lb (approximately 8 cups) bag powdered sugar
2 teaspoons vanilla extract
3-4 tablespoons milk

Equipment Needed

Electric mixer (stand mixer or hand mixer)
Large mixing bowls
Six small bowls (for dividing and coloring batter)
Three 8-inch round cake pans
Cooking spray or butter and flour for greasing pans
Measuring cups and spoons
Rubber spatula or scraper
Wire cooling racks
Serrated knife (for leveling cakes, optional)
Offset spatula or butter knife (for frosting)
Serving plate or cake stand

Instructions

Prepare the Oven and Pans: Begin by preheating your oven to 350°F (175°C). Thoroughly spray three 8-inch round cake pans with cooking spray. For extra assurance against sticking, you can also lightly flour the greased pans.
Mix the Cake Batter: In a large bowl, combine the Betty Crocker Supermoist White Cake Mix, 2 cups of water, 1 cup of vegetable oil, and the 6 large eggs. Beat the ingredients with an electric mixer on low speed for 30 seconds to incorporate them. Then, increase the speed to medium and continue beating for 2 minutes, scraping down the sides of the bowl occasionally to ensure everything is evenly mixed.
Divide and Color the Batter: Once the batter is smooth and well-combined, divide it evenly among six small bowls. You should aim for approximately 1 1/3 cups of batter in each bowl.
Create the Rainbow Hues: This is where the magic truly begins. Using your Betty Crocker Gel Food Coloring, carefully tint the batter in each bowl.
- In one bowl, add enough blue food coloring to achieve a vibrant blue.
- In another bowl, add enough red food coloring for a brilliant red.
- In a third bowl, use green food coloring to create a cheerful green.
- To make orange, combine red and yellow food coloring in a fourth bowl until you achieve your desired shade.
- For purple, mix blue and red food coloring in a fifth bowl.
- The remaining bowl will be your yellow.
  Gently stir the food coloring into each bowl of batter until the color is uniform and no streaks remain. Be mindful not to overmix, as this can affect the cake’s texture.
Bake the First Three Layers: Refrigerate three of the colored batter bowls (for example, the purple, blue, and green). Pour the remaining three colors of batter (yellow, orange, and red) into your prepared cake pans, dividing them equally. Bake for 18 to 20 minutes, or until a wooden skewer or toothpick inserted into the center of the cakes springs back when touched lightly and the cake edges begin to pull away from the sides of the pan.
Cool the First Layers: Allow the baked cake layers to cool in their pans for 10 minutes. Then, carefully remove them from the pans and transfer them to wire cooling racks to cool completely.
Bake the Remaining Layers: While the first set of layers are cooling, wash your cake pans thoroughly. Bake and cool the remaining three cake layers (purple, blue, and green) following the same directions as above.
Prepare the Buttercream Frosting: In a large bowl, beat the 1 cup of shortening and 1 cup of softened butter with an electric mixer on medium speed until the mixture is light yellow and fluffy. This process aerates the fats, creating a stable and smooth frosting base.
Incorporate Powdered Sugar and Vanilla: With the mixer on low speed, gradually beat in the 2 lb bag of powdered sugar. This helps to prevent a cloud of sugar from erupting into your kitchen. Once the sugar is mostly incorporated, beat in the 2 teaspoons of vanilla extract.
Achieve Frosting Consistency: Add the milk, 1 tablespoon at a time, while continuing to beat on low speed. Continue adding milk and beating until the frosting is smooth and reaches your desired consistency. Once smooth, increase the mixer speed to high and beat for an additional 2-3 minutes until the frosting is light and fluffy.
Level the Cake Layers (Optional): If your cake layers have domed tops, you can carefully trim them with a serrated knife to create flat surfaces. This will make stacking and frosting much easier, resulting in a more professional finish.
Assemble the Rainbow: On your serving plate or cake stand, begin by placing the purple cake layer. Spread a layer of the buttercream frosting evenly over the top, extending it to within 1/4 inch of the edge of the cake.
Layer the Colors: Continue layering the remaining cake layers in rainbow order: blue, then green, then yellow, then orange, and finally the red cake layer on top. Spread frosting between each layer.
Crumb Coat the Cake: Apply a thin, light coat of frosting over the entire top and sides of the cake. This is known as a “crumb coat” and its purpose is to seal in any loose crumbs, preventing them from appearing in your final, smooth frosting layer. Chill the cake for about 15-30 minutes if time permits, to allow the crumb coat to set.
Final Frosting: Once the crumb coat is set, generously frost the top and sides of the cake with the remaining buttercream frosting, smoothing it with an offset spatula or butter knife for a polished look.

Expert Tips & Tricks

Gel Food Coloring is Key: For the most vibrant and true rainbow colors without adding too much extra liquid to your batter, always opt for gel food coloring. Liquid food coloring can dilute your batter and affect the cake’s texture.
Don’t Overmix: Overmixing cake batter can develop the gluten too much, leading to a tough cake. Mix just until the ingredients are combined.
Room Temperature Ingredients for Frosting: Ensure your butter and shortening are truly softened to room temperature for the smoothest, most easily incorporated buttercream. Cold fats won’t emulsify properly.
Sift Your Powdered Sugar: While the recipe calls for a bag, sifting your powdered sugar before adding it to the butter and shortening can help eliminate any lumps and create an even silkier frosting.
Make Ahead Magic: You can bake the cake layers a day in advance. Once completely cooled, wrap them tightly in plastic wrap and store them at room temperature. The frosting can also be made a day ahead and stored in an airtight container in the refrigerator; just let it soften slightly and re-whip before using.
Consistent Layer Thickness: If you’re aiming for perfect evenness, consider using a kitchen scale to divide your batter among the bowls. This ensures each layer will be the same weight and therefore bake more uniformly.

Serving & Storage Suggestions

This Rainbow Layer Cake is best served at room temperature, allowing the flavors and textures to shine. To serve, simply cut through the vibrant layers with a sharp knife. Store any leftover cake in an airtight container at room temperature for up to 2 days. If you need to store it for longer, it can be refrigerated for up to 4 days, though the frosting may firm up. For freezing, wrap individual slices or the whole cake tightly in plastic wrap, then in aluminum foil. It can be frozen for up to 2 months. Thaw overnight in the refrigerator before bringing to room temperature to serve.

Nutritional Information

Nutrient	Amount per Serving	% Daily Value
Calories	1376 kcal
Calories from Fat		674 g
Total Fat	74.9 g	115%
Saturated Fat	22.3 g	111%
Cholesterol	161.1 mg	53%
Sodium	893.2 mg	37%
Total Carbohydrate	171.3 g	57%
Dietary Fiber	0.9 g	3%
Sugars	145 g	580%
Protein	8.7 g	17%

Note: Nutritional information is an estimate and can vary based on specific ingredients and brands used.

Variations & Substitutions

Lemon Zest Infusion: For a brighter, more citrusy cake, add the zest of 1-2 lemons to the cake batter before baking. This pairs beautifully with the sweetness of the frosting.
Vanilla Bean Speckled Frosting: Instead of vanilla extract, scrape the seeds from 1 vanilla bean and incorporate them into your buttercream for a more intense vanilla flavor and beautiful speckles.
Cream Cheese Frosting: For a tangier frosting, consider a cream cheese frosting. You’ll typically need about 8 ounces of cream cheese, softened, whisked with the butter and shortening, then combined with the powdered sugar and vanilla. Adjust milk as needed for consistency.
Dark Chocolate Cake Layers: If you’re a chocolate lover, you could substitute one of the cake mix boxes with a Betty Crocker Supermoist Chocolate Fudge cake mix for a delightful surprise within the rainbow.

FAQs

Q: Why are there six colors but only three cake pans?
A: You’ll bake three layers at a time, using three pans. Once those are cooled and removed, you’ll wash the pans and bake the remaining three layers. This ensures you have six distinct, colorful cake layers to assemble.

Q: How do I get such vibrant colors without making the batter too wet?
A: It’s crucial to use gel food coloring. Unlike liquid food coloring, gel colors are highly concentrated and add minimal moisture, allowing you to achieve intense hues without altering the batter’s consistency.

Q: My cake layers always seem to dome in the center. How can I prevent this?
A: While some doming is natural, you can minimize it by not overmixing the batter and ensuring your oven temperature is accurate. If they do dome, leveling them with a serrated knife before frosting is the simplest solution.

Q: Can I make this cake ahead of time?
A: Absolutely! The cake layers can be baked and cooled a day in advance, then stored tightly wrapped. The frosting can also be made ahead and refrigerated, then re-whipped before use.

Q: What’s the best way to store leftover rainbow cake?
A: Store leftover cake in an airtight container at room temperature for up to two days. For longer storage, refrigerate for up to four days.

Final Thoughts

This Rainbow Layer Cake is more than just a dessert; it’s an experience. It’s a celebration of color, a testament to simple joy, and a truly show-stopping centerpiece for any occasion. The anticipation as you slice into its vibrant layers, revealing a spectrum of hues, is a delight that never fades. Whether for a birthday, a holiday, or simply a Tuesday that needs a bit more sparkle, this cake is sure to bring smiles and a touch of magic to your table. Gather your ingredients, embrace the colorful journey, and savor every delicious, radiant bite.

Rainbow Layer Cake With Buttercream Frosting Recipe