Moist Rainbow Sheet Cake Recipe with Easy Creamy Buttercream Frosting

Written by

mandy

Posted on January 6, 2026

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Dessert Recipes

January 6, 2026

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Let me tell you, the scent of vanilla and cocoa mingling with bright bursts of colorful batter baking in the oven is enough to make anyone’s mouth water. The first time I baked this moist rainbow sheet cake with its creamy buttercream frosting, I was instantly hooked. It was one of those rare baking moments where everything just clicks—the kind of moment where you pause, take a deep breath, and just smile because you know you’re onto something truly special.

Years ago, when I was knee-high to a grasshopper, cakes were simple affairs—chocolate or vanilla, maybe a sprinkle of funfetti if we were lucky. But stumbling upon this recipe on a rainy weekend changed all that. Honestly, I wish I’d discovered this colorful beauty years ago. My family couldn’t stop sneaking pieces off the cooling rack (and I can’t really blame them). It’s dangerously easy to make yet delivers pure, nostalgic comfort with every forkful.

This moist rainbow sheet cake recipe with creamy buttercream frosting is perfect for brightening up birthday parties, potlucks, or just surprising your kids with a sweet treat after school. After testing it multiple times (in the name of research, of course), it’s become a staple for family gatherings and gifting. It feels like a warm hug wrapped in layers of vibrant, tender cake and rich frosting—you’re going to want to bookmark this one.

Why You’ll Love This Recipe

Here’s the lowdown on why this moist rainbow sheet cake with creamy buttercream frosting stands out from the crowd. After numerous baking trials and tweaks, I’ve learned what makes this recipe a winner every time:

Quick & Easy: Comes together in under an hour, perfect for busy weeknights or last-minute celebrations.
Simple Ingredients: No fancy grocery store trips needed; you likely already have everything in your pantry.
Perfect for Parties: Great for birthdays, potlucks, or any occasion that calls for a splash of color and sweetness.
Crowd-Pleaser: Always gets rave reviews from kids and adults alike thanks to its moist crumb and silky frosting.
Unbelievably Delicious: The balance between the tender layers and creamy buttercream is pure comfort food perfection.

This isn’t just another rainbow cake. The batter is perfectly balanced to stay moist without being too dense or crumbly, and the buttercream frosting is whipped just right to be creamy but not overly sweet. You know what makes this recipe different? I blend in a touch of sour cream for that extra moist crumb and use a little almond extract alongside vanilla to add depth—trust me, it’s magic.

It’s the kind of recipe that makes you close your eyes after the first bite and say, “Yep, that’s the one.” Whether you’re impressing guests without stress or turning a simple day into something memorable, this cake delivers every single time.

What Ingredients You Will Need

This recipe uses simple, wholesome ingredients to deliver bold flavor and a satisfying, tender texture without the fuss. Most are pantry staples, and the color magic comes from basic food coloring you can pick up anywhere.

For the Cake Batter:

All-purpose flour – 3 cups (360 g) (for best texture, I prefer King Arthur flour)
Baking powder – 1 tablespoon
Baking soda – 1 teaspoon
Salt – ½ teaspoon
Unsalted butter – 1 cup (227 g), softened (adds richness and moisture)
Granulated sugar – 2 cups (400 g)
Large eggs – 4, room temperature
Buttermilk – 1 cup (240 ml), room temperature (or use milk + 1 tbsp vinegar as a substitute)
Sour cream – ½ cup (120 ml), room temperature (keeps cake moist)
Pure vanilla extract – 2 teaspoons
Almond extract – ½ teaspoon (optional, for subtle depth)
Gel food coloring – red, orange, yellow, green, blue, and purple (use gel for vibrant, not liquid)

For the Creamy Buttercream Frosting:

Unsalted butter – 1 cup (227 g), softened
Powdered sugar – 4 cups (480 g), sifted
Heavy cream – 2-3 tablespoons (30-45 ml) (use more to thin out if needed)
Pure vanilla extract – 2 teaspoons
Pinch of salt (balances sweetness)

If you want a dairy-free version, swap butter with vegan margarine and heavy cream with coconut cream, and use a dairy-free sour cream alternative. In summer, fresh berries on top make a beautiful garnish and add a fresh note.

Equipment Needed

9×13-inch (23×33 cm) sheet pan – essential for the classic sheet cake shape
Mixing bowls – at least two, one for dry and one for wet ingredients
Electric mixer or stand mixer – makes creaming butter and sugar a breeze
Spatula – for folding and scraping down the sides
Measuring cups and spoons – accurate measurements make all the difference
Whisk – handy for combining dry ingredients
Offset spatula or butter knife – perfect for spreading frosting evenly

If you don’t have a stand mixer, a hand mixer works just fine. For budget-friendly options, basic silicone spatulas and stainless steel bowls get the job done without breaking the bank. Keep your mixer beaters clean and dry to avoid any funky frosting texture—you know, little things that pay off big time!

Preparation Method

Preheat and prep: Preheat your oven to 350°F (175°C). Grease your 9×13-inch (23×33 cm) sheet pan with butter or non-stick spray and lightly flour it. This prevents sticking and helps the cake come out cleanly.
Mix dry ingredients: In a medium bowl, whisk together 3 cups (360 g) all-purpose flour, 1 tablespoon baking powder, 1 teaspoon baking soda, and ½ teaspoon salt. Set aside.
Cream butter and sugar: In a large bowl, use your mixer to beat 1 cup (227 g) softened unsalted butter and 2 cups (400 g) granulated sugar on medium speed for about 3-4 minutes until light and fluffy. This step is key to a tender crumb.
Add eggs and extracts: Beat in 4 large eggs, one at a time, making sure each is fully incorporated. Then add 2 teaspoons vanilla extract and ½ teaspoon almond extract (if using). Mix until smooth.
Alternate adding dry and wet: Reduce mixer speed to low. Add the dry ingredients in three parts, alternating with 1 cup (240 ml) buttermilk and ½ cup (120 ml) sour cream in two parts. Start and end with dry ingredients. Mix just until combined—overmixing can toughen the cake.
Divide and color batter: Divide the batter evenly into six small bowls. Add a few drops of gel food coloring to each: red, orange, yellow, green, blue, and purple. Stir gently until the colors are vibrant and even.
Layer the batter: Pour each colored batter one at a time into the prepared pan, spreading gently with a spatula to create even layers. Don’t worry if the edges blend a little; that’s part of the charm.
Bake: Bake for 30-35 minutes or until a toothpick inserted in the center comes out clean. The cake should spring back lightly when pressed. Let it cool completely in the pan on a wire rack before frosting.
Make the buttercream: While the cake cools, beat 1 cup (227 g) softened unsalted butter on medium speed until creamy (about 2 minutes). Gradually add 4 cups (480 g) powdered sugar, alternating with 2-3 tablespoons (30-45 ml) heavy cream. Beat until fluffy and smooth. Mix in 2 teaspoons vanilla extract and a pinch of salt.
Frost the cake: Spread the buttercream evenly over the cooled cake with an offset spatula. For a fun touch, swirl with the spatula to create peaks and valleys. Chill for 15 minutes if frosting feels too soft.

Cooking Tips & Techniques

Getting this moist rainbow sheet cake just right takes a few insider tricks. First, always use gel food coloring for those bright, true rainbow hues. Liquid colorings can thin your batter, messing with the texture.

When mixing, don’t rush the creaming of butter and sugar—it’s what traps air and gives the cake its lightness. Also, alternating dry and wet ingredients prevents lumps and keeps the batter smooth.

Be careful not to overmix once the flour is in. Overdoing it creates a tough cake, and let’s face it, nobody wants that. If you find your buttercream is too stiff, add a splash more heavy cream, but add it slowly—you want fluffy, not runny.

Lastly, timing is everything. Bake just until a toothpick comes out clean; overbaking dries the cake out. I usually set a timer for 30 minutes and check every few minutes after that. Multitasking helps too—make your frosting while the cake cools to save time.

Variations & Adaptations

This recipe is super flexible, and I love mixing it up depending on the occasion or dietary needs. Here are a few variations I’ve tried and loved:

Gluten-Free: Swap the all-purpose flour for a 1:1 gluten-free baking blend. The texture stays surprisingly moist and tender.
Vegan Version: Use flax eggs (1 tablespoon flaxseed meal + 3 tablespoons water per egg), plant-based butter, and coconut cream in place of dairy. The frosting can be made with powdered sugar and vegan butter.
Chocolate Rainbow: Add ¼ cup (20 g) cocoa powder to each colored batter for a slight chocolate twist. It’s subtle but adds a rich undertone.
Fruit-Infused: Fold in finely chopped strawberries or blueberries into each colored layer before baking for a burst of fresh flavor.

For different cooking methods, you can bake this cake in two 9-inch round pans for a layer cake version—just reduce the baking time to 25-30 minutes. Want a fun twist? Try using natural food colors from beet juice or matcha powder for a more earthy flavor profile.

Serving & Storage Suggestions

This rainbow sheet cake is best served at room temperature so the buttercream stays silky and soft. Slice it into generous squares and plate with a dollop of whipped cream or fresh berries for a party-ready presentation.

Pairs beautifully with a cold glass of milk, freshly brewed coffee, or a fruity iced tea. For a grown-up touch, a splash of flavored liqueur in your coffee works wonders.

To store, cover leftovers tightly with plastic wrap or place in an airtight container. Keep refrigerated for up to 4 days. The cake actually tastes better after a day as the flavors meld together. You can freeze unfrosted cake layers for up to 3 months—just thaw completely before frosting.

Reheat slices gently in the microwave for 10-15 seconds if you prefer warm cake. Just be careful not to melt the frosting!

Nutritional Information & Benefits

Each serving of this moist rainbow sheet cake delivers approximately 350 calories, with 12 grams of fat, 50 grams of carbohydrates, and 4 grams of protein (based on 12 servings). While it’s a treat, the cake includes wholesome ingredients like buttermilk and sour cream that add moisture without excess fat.

Vanilla and almond extracts add flavor without calories, and using gel food coloring means no artificial sugars are introduced. You can swap in whole wheat flour for a bit more fiber, or use a sugar substitute to lower the sugar content.

Keep in mind this recipe contains common allergens like eggs, dairy, and gluten, but substitutions can be made to accommodate dietary restrictions without sacrificing flavor.

Conclusion

In a nutshell, this moist rainbow sheet cake with creamy buttercream frosting is a keeper. It combines simplicity with show-stopping color and taste, making it a perfect choice for celebrations or anytime you want to bring a little joy to the table. Customize it to your heart’s desire, whether that’s making it gluten-free, vegan, or adding your own twist of flavor.

Personally, this cake warms my heart every time I bake it—there’s just something about those vibrant layers paired with smooth frosting that feels like a party in every bite. I hope you’ll try it, share it, and make it your own. If you do, please leave a comment or share how you adapted it—I love hearing your baking stories!

So go ahead, grab your mixing bowl, and get ready to wow your family and friends with this colorful, delicious treat. Happy baking!

FAQs

Can I use liquid food coloring instead of gel?

You can, but gel food coloring is best for vibrant colors without thinning the batter. Liquid colors may make the batter runnier and affect texture.

How do I store leftover cake?

Store it in an airtight container in the refrigerator for up to 4 days. Bring to room temperature before serving for the best taste.

Can I make this cake ahead of time?

Absolutely! You can bake the cake layers a day ahead and keep them wrapped tightly at room temperature or refrigerate. Frost the cake the next day for freshest results.

Is there a way to make the frosting less sweet?

Try reducing the powdered sugar slightly or adding a pinch more salt to balance sweetness. You can also add a teaspoon of lemon juice for a subtle tang.

What if I don’t have buttermilk?

Simply add 1 tablespoon of white vinegar or lemon juice to 1 cup of milk, let it sit for 5 minutes, and use as a buttermilk substitute.

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