Rainbow Sprinkle Cake with Vanilla Buttercream

There's something magical about a cake covered in rainbow sprinkles. Maybe it's the way those tiny bursts of color instantly transport you back to childhood birthday parties, or how they make even a regular Tuesday feel like a celebration. This Rainbow Sprinkle Cake with Vanilla buttercream is exactly that kind of recipe—the one that makes everyone smile before they even take a bite.

I'll be honest: I didn't grow up making fancy layer cakes or spending hours in the kitchen perfecting frosting techniques. But this cake? It's different. It's straightforward, forgiving, and honestly fun to make. The secret ingredient here is kefir, which keeps everything incredibly moist while adding a subtle tang that balances the sweetness perfectly. And before you worry about finding specialty ingredients, you can grab everything at your regular grocery store.

Jump To Recipe

• Why You'll Love This Rainbow Sprinkle Cake with Vanilla Frosting
• What You'll Need
• Getting Started
• Bringing It Together
• The Waiting Game
• Creating the Perfect Vanilla Buttercream
• Decorating Your Masterpiece
• Serving and Storage Tips
• Make It Your Own
• Frequently Asked Questions
• Conclusion
• Rainbow Sprinkle Cake with Vanilla Buttercream

Why You'll Love This Rainbow Sprinkle Cake with Vanilla Frosting

Let me tell you why this cake has earned a permanent spot in my recipe rotation. First, it's a one-bowl wonder for the cake itself—less cleanup means more time enjoying what you've made. Second, it's genuinely foolproof. The batter comes together in about ten minutes, and even if you're not an experienced baker, you'll feel like a pro.

The texture is what really sets this apart. Thanks to the kefir, you get this tender, fluffy crumb that stays moist for days (if it lasts that long). And those rainbow sprinkles? They're folded right into the batter, creating little pockets of color throughout. Top it with silky vanilla buttercream, and you've got a vanilla cake that looks like it came from a bakery but required minimal effort.

This is also the perfect cake for anyone who wants something festive without complicated decorating skills. No piping bags required, no fondant nightmares—just spread, swirl, and sprinkle.

What You'll Need

The ingredient list here is refreshingly simple. You probably have most of these items in your pantry right now. All-purpose flour forms the base, while baking powder and baking soda work together to give you that perfect rise. A touch of salt enhances all the flavors without making anything taste salty.

For sweetness, regular granulated sugar does the job beautifully. I use vegetable oil instead of butter in the cake itself because it creates a more tender texture and keeps the cake moist longer—trust me on this one. One egg binds everything together, and vanilla extract brings that classic bakery flavor we all love.

Now, here's where things get interesting: Lifeway Rainbow Cake Lowfat Kefir. If you haven't baked with kefir before, you're in for a treat. It's similar to buttermilk but with probiotics, and it makes cakes incredibly soft. The rainbow cake variety adds a fun twist, though plain kefir works great too. A splash of hot water thins the batter just enough for an even bake, and of course, rainbow sprinkles are non-negotiable—go for jimmies or quins, whichever makes your heart happy.

The vanilla buttercream frosting is equally simple: butter, powdered sugar, vanilla, and a splash of milk or cream. That's it. No complicated techniques or hard-to-find ingredients.

Getting Started

Before you dive in, preheat your oven to 350°F. I can't tell you how many times I've mixed an entire cake batter only to realize I forgot this step—don't be me. Grease an 8-inch square pan and line it with parchment paper. The parchment makes lifting the cake out later so much easier, and it prevents any sticking disasters.

Grab a large mixing bowl and whisk together your dry ingredients: flour, baking powder, baking soda, and salt. Give it a good whisk to make sure everything's evenly distributed. No sifting required here—we're keeping things simple.

In a separate medium bowl, combine your wet ingredients. Whisk together the sugar, oil, vanilla, egg, and kefir until everything looks smooth and unified. The mixture might seem a bit thin, and that's perfectly fine.

Bringing It Together

Pour your wet ingredients into the dry ingredients and stir gently with a spatula or wooden spoon. Here's a tip I learned the hard way: don't overmix. Stir just until you see a few flour streaks remaining—this keeps your cake tender instead of tough. Then add the hot water and mix until just combined. The batter will be fairly thin, which might feel wrong, but it's exactly what you want for a moist cake.

Fold in those rainbow sprinkles last. Be gentle here so they don't bleed their colors into the batter (though honestly, if they do, it just adds to the fun).

Pour everything into your prepared pan and give it a gentle tap on the counter to release any air bubbles. Slide it into your preheated oven on the middle rack. This positioning ensures even heat distribution, so you don't end up with a dome-shaped top or burnt edges.

The Waiting Game

Baking time is about 35 to 45 minutes, but every oven is slightly different. Start checking around the 35-minute mark with a toothpick inserted into the center. If it comes out clean or with just a few moist crumbs, you're done. If you see wet batter, give it another five minutes and check again.

Here's something I wish someone had told me when I started baking: the cake will continue cooking slightly after you remove it from the oven. So if your toothpick comes out with just a tiny bit of moisture, that's actually perfect. An overbaked cake is dry and sad, and nobody wants that.

Let the cake cool completely in the pan. I know waiting is hard—believe me, I've tried frosting a warm cake before, and the results were... not Instagram-worthy. The frosting just melts right off. Give it at least 30 minutes, or better yet, pop it in the fridge for 15 minutes to speed things up.

Creating the Perfect Vanilla Buttercream

While your cake cools, make your homemade frosting. This is possibly the easiest buttercream you'll ever make. Start with room-temperature butter—this is crucial. Cold butter won't mix properly, and melted butter will make your frosting too thin.

Beat the butter in a bowl until it's creamy and smooth, about two minutes with a hand mixer or stand mixer. Then gradually add your powdered sugar, about half a cup at a time. This prevents the sugar cloud that inevitably coats your kitchen if you dump it all in at once (speaking from experience here).

Add the vanilla extract and start with just one tablespoon of milk. Mix everything together, then assess the consistency. Want it thicker for spreading? Add more powdered sugar. Too thick? Add another tablespoon of milk. The beauty of buttercream is that it's incredibly forgiving and easy to adjust.

Decorating Your Masterpiece

Once your cake is completely cool, lift it out of the pan using the parchment paper edges. Place it on your serving plate or cake stand. Now comes the fun part: frosting.

Spread your vanilla buttercream over the top of the cake using an offset spatula or butter knife. Don't worry about making it perfect—rustic cakes are trendy for a reason. If you want to create that gorgeous tie-dye effect I mentioned, place tiny drops of food coloring (I like using three or four different colors) randomly across the frosting. Then use your knife or spatula to gently swirl them together. Don't overwork it, or the colors will muddy together. A few quick swirls create that beautiful marbled look.

Finish with more rainbow sprinkles on top. You really can't use too many—this is a celebration cake, after all. The sprinkles add texture and make every bite a little more joyful.

Serving and Storage Tips

This square cake cuts beautifully into nine generous squares or twelve more modest pieces. I love serving it at room temperature with a cold glass of milk or a hot cup of coffee. It's perfect for birthday parties, potlucks, or those days when you just need a slice of happiness.

If you somehow have leftovers (which rarely happens in my house), store the cake covered at room temperature for up to three days. The kefir keeps it moist, so you won't have that dry, crumbly cake situation. You can also refrigerate it for up to five days, though I find the frosting firms up a bit in the cold. Just let it sit out for about 20 minutes before serving to bring it back to its optimal texture.

Want to make this ahead? Bake the cake, let it cool completely, wrap it tightly in plastic wrap, and freeze it for up to three months. Thaw it in the fridge overnight, then frost and decorate before serving.

Make It Your Own

One of the things I love most about this recipe is how adaptable it is. While this version celebrates rainbow sprinkles and vanilla flavor, you can absolutely customize it. Try chocolate sprinkles for a cookies-and-cream vibe, or add a teaspoon of almond extract to the frosting for something different.

If you can't find rainbow cake kefir, plain or vanilla kefir works perfectly—you'll still get that amazing texture. In a pinch, you can even substitute buttermilk, though you'll miss out on those probiotic benefits.

For a special occasion, transform this into a layer cake by baking two cakes and stacking them with frosting in between. It takes the celebration factor up several notches without much additional effort.

Frequently Asked Questions

Conclusion

This Rainbow Sprinkle Cake with Vanilla frosting proves that baking doesn't have to be complicated to be special. It's the kind of recipe that makes you feel capable and creative, whether you're new to baking or have been doing it for years. Those rainbow sprinkles mixed throughout the batter create little moments of color and fun in every bite, while the tender, moist crumb makes it genuinely delicious—not just pretty to look at.

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