Single-Layer Funfetti Cake with Rainbow Sprinkles

Bring a little fun to your next dessert with this 6-inch single-layer funfetti cake! It stays moist and tender and is mixed with a handful of rainbow jimmies. For added vanilla flavor, pair it with this small-batch vanilla flour buttercream and top it with a blend of your favorite sprinkles! It's another easy, delicious single-layer cake you're sure to love!

8 Reasons to Love This Recipe

1. It's easy to make.
2. This makes one 6-inch single-layer funfetti cake, but it's thick enough to slice into two layers!
3. It serves up to 6 people.
4. It's moist and tender, thanks to the buttermilk!
5. Rainbow jimmies (or sprinkles) make desserts fun and bring smiles to people's faces!
6. It's paired with a vanilla buttercream that is NOT made with powdered sugar.
7. It's wonderful for small dinner parties, birthdays, an intimate dinner, or a really nice way to treat yourself!
8. You can make your own rainbow sprinkle mix for decorating!

What You'll Need

To make this moist and tender vanilla funfetti cake, you'll need these ingredients:

• Cake Flour
• Baking Powder
• Salt
• Unsalted Butter
• Granulated Sugar
• 1 Egg
• Vanilla Extract
• Buttermilk
• Rainbow Jimmies (or sprinkles), plus extra for decorating (see below)

Substitutions

Cake flour substitute. If cake flour is hard to find where you live, use the substitute shown below.

Whole Milk. You can use whole milk if you don't have buttermilk on hand. For a texture closer to buttermilk, add two teaspoons of lemon juice to the 1/3 measuring cup first, then fill the rest of the cup with whole milk. Pour it into a small glass bowl and let it thicken for about 5 minutes.

I did not test this recipe with alternative flours, egg substitutes, dairy-free alternatives, or other cake pans.

Homemade Cake Flour Substitute

No cake flour in the pantry? You can make your own! You only need all-purpose flour, cornstarch, and a sifter!

To make homemade cake flour:

1. Add one tablespoon of cornstarch to a ½ cup measuring cup.
2. Fill the rest of the measuring cup with all-purpose flour.
3. Run the mixture through a sifter. One pass is good, but two is even better!

If you want extra on hand, double the recipe above. Store it in an airtight container at room temperature or, my preference, in the freezer.

What Is Flour Buttercream?

Flour buttercream, also called Ermine buttercream or boiled milk frosting, is made without powdered sugar.

Its ingredients are all-purpose flour, granulated sugar, salt, milk, vanilla extract, and unsalted butter.

The process takes a bit more time, but you end up with a less sweet buttercream that resembles Swiss meringue, with the creaminess of classic American buttercream.

How to Make Small-Batch Vanilla Flour Buttercream

This buttercream comes together in two parts and takes some time.

If you'd rather make my small-batch vanilla buttercream with powdered sugar, check out my Small Batch Vanilla Cupcakes recipe.

STEP ONE. Whisk the all-purpose flour, granulated sugar, and salt together. Add the milk and whisk again.

STEP TWO. Over low-medium heat, bring the mixture almost to a boil while stirring constantly with a spatula. Scrape the bottom of the pan too. It will thicken to a paste-like consistency and look wet and glossy.

STEP THREE. Take it off the heat and keep stirring and scraping for another 1-2 minutes. This releases some heat and dulls the shine.

STEP FOUR. Spread the mixture onto a plate (one with a rim works best) and press plastic wrap directly onto the surface right away so no skin forms. Let it reach room temperature before the next step.

Tip: To speed things up, chill it in the refrigerator, then take it out and let it come back to room temperature. Both the thickened mixture and the butter need to be at room temperature.

STEP FIVE. Make sure the butter is at room temperature and cut into cubes. Beat it with a stand or hand mixer for 2-3 minutes, until pale and fluffy.

STEP SIX. Add the paste one spoonful at a time, not all at once. Let each spoonful blend in before adding the next. When it's all in, scrape the bowl, add the vanilla extract, and mix on medium-high.

You can make either the thickened flour mixture or the flour buttercream 3-5 days ahead. Store it in the refrigerator, then bring it to room temperature before using.

Before using the vanilla flour buttercream, whip it again with the mixer to bring it back to life.

Make Your Own Sprinkle Mix

Want to switch up the sprinkles on your 6-inch funfetti cake? Try this combination! You can mix and match any sprinkles in endless ways. For this mix, I used these 3:

• Rainbow Jimmies (or Rainbow Sprinkles)
• Rainbow Nonpareils
• Rainbow Confetti Sprinkles

The brand I used has natural coloring, so it's not super bold or bright. The colors are more muted.

Add a small amount to a jar with a lid (a ball canning jar works well), screw the lid on tight, and give it a shake. Ta-da, your own sprinkle mix!

FAQs

Do you recommend using a 6-inch by 2-inch cake pan or a 6-inch by 3-inch cake pan?

Because this cake is thicker, I suggest the 6-inch by 3-inch cake pan. If you use a 6-inch by 2-inch pan, the batter will most likely rise right up to the rim.

What’s the best knife for slicing this funfetti cake into two layers?

I always recommend a serrated knife for slicing.

How much vanilla flour buttercream does this make?

This small-batch recipe makes about 1 1/4 cups of frosting, enough to cover the whole cake. If you slice the cake into two layers, you'll have enough for a thin layer in between.

Why did my flour buttercream come out thin and runny?

It’s more than likely that you did not let your flour mixture cool 100% before mixing it with the butter. Likewise, the same thing can occur if your butter is too soft.

My flour buttercream is grainy and not at all smooth.

The flour mixture may not have reached room temperature after cooling. If it's still cool and meets cold butter, the frosting can turn out grainy. Both the butter and the flour mixture need to be at room temperature.

What sprinkle combination did you use for your cake?

I used a mix of rainbow sprinkles, rainbow nonpareils, and rainbow confetti sprinkles. You'll find them linked in the baking tools section below!

Essential Cake Making Tools

More Small-Batch Dessert Recipes

If you make this single-layer funfetti cake, I'd love to hear how it turned out! Leaving a comment and star rating below helps me and other bakers. Thanks!