The Best Funfetti Blondies (Birthday Cake Batter Blondies)

This funfetti blondies recipe features deliciously chewy brown sugar and vanilla-laced cake batter-flavored cookie bars. Fun, festive rainbow sprinkles and creamy vanilla frosting take it over the top!

Blondies are a deliciously fun treat even when they’re not funfetti flavor. But when you make them cake batter flavor and add colorful rainbow sprinkles, it’s really a party!

Once you master the basic method for making blondies you’ll see how quick and easy they are. Without the frosting, these whip up in about 30 minutes including bake time with just one bowl and no need for a stand mixer.

And you’ll think of a ton of different ways to customize them because the sky is the limit! Dark chocolate chips, white chocolate chips, chopped nuts, dried fruit, etc. It all works.

Like other bar cookies, these are the perfect treat for potlucks and parties. And funfetti sprinkle blondies can also make a stand as birthday cake blondies, which makes them perfect for birthday celebrations. But don’t wait until then to make them!

Blondies are the perfect treat on a random Tuesday evening when you want something a sweet without having to spend hours in the kitchen. And funfetti makes them fun!

Why You’ll Love This Recipe

• They’re delicious. Rich, chewy, buttery brown sugar blondies are made fun and colorful with rainbow sprinkles! Sweet vanilla buttercream is optional, but makes them decadent.
• Happy birthday. Funfetti blondies are great for a birthday celebration. Like any funfetti, cake batter-flavored treat, this is the perfect birthday dessert!
• Dessert doesn’t get any easier. However, unlike baking up a funfetti birthday cake, blondies are much quicker and easier to make!

The Best Funfetti Blondies Recipe

Ingredients

In these sections, I explain the ingredients and give substitution ideas. For the full recipe (including ingredient amounts), see the recipe card below.

Funfetti Blondies Ingredients

• Unsalted butter – for rich flavor and gooey texture
• Granulated sugar – we use a mixture of granulated white sugar and brown sugar for the perfect sweetness level
• Light brown sugar – a touch of light brown sugar adds complex notes of molasses, and helps make our blonde brownies really chewy
• Egg – the binder
• Vanilla – for flavor and aroma
• Cake batter flavor – just a touch of cake batter flavor gives these blondies a funfetti birthday cake flavor
• Flour – use all-purpose flour
• Salt – a natural flavor enhancer
• Rainbow sprinkles – rainbow sprinkles are perfect for birthday celebrations, but you can swap out the sprinkles for any holiday (for example, use red and green sprinkles for Christmas)

Vanilla Frosting Ingredients

• Unsalted butter – butter and powdered sugar are the base of this easy American buttercream that whips up in just a couple minutes
• Powdered sugar – powdered sugar blends really well so you end up with a smooth frosting
• Heavy whipping cream – makes this buttercream velvety and creamy; you can also use milk if that’s what you have on hand
• Vanilla – for flavor and aroma; if you have vanilla bean paste on hand, you can use that instead for pretty flecks of vanilla
• Salt – this balances the flavor so our buttercream frosting isn’t too sweet

How to Make Cake Batter Funfetti Blondies From Scratch

Step 1: Make the Blondie Batter

Preheat the oven to 350F.

Melt the butter in a large bowl in the microwave and let it cool for about 30 seconds to 1 minute. Whisk in the granulated sugar and brown sugar until well-mixed. Whisk in the egg, vanilla extract, and cake batter flavor. Add the flour and salt and stir until combined, being careful not to over-mix. Fold in the rainbow sprinkles.

Step 2: Get Ready to Bake

Line an 8 by 8-inch baking pan with 2 pieces of parchment paper so it hangs over all 4 sides. Transfer the blondie batter to the prepared pan, spreading it out evenly.

Step 3: Bake and Cool

Bake until the outside looks light golden, but the inside looks doughy, about 22 to 25 minutes at 350F.

Let the blondies cool for about 10 minutes in the pan, and then remove them to a wire rack to cool to room temperature.

Step 4: Frost and Decorate

While the blondies are cooling, make the frosting.

Add all ingredients to a large bowl. Use a handheld electric mixer to beat until well-combined. You may need to add a bit more heavy whipping cream to achieve the right consistency.

Frost the blondies once they’re cooled. Before the frosting sets, top with rainbow sprinkles.

How to Store Blondies

Once they’re cool, wrap blondies well and then store them for up to 4 days at room temperature or up to 1 week in the fridge.

Tips

• The butter should still be hot. After you melt the butter, only let it cool for about 30 seconds to 1 minute before whisking in the sugar. This will help make sure you get a gorgeous crackled top!
• Instead of cake batter flavoring. If you can’t find cake batter flavor, you can substitute with a combination of butter flavor and almond extract. (About 1/2 teaspoon butter flavor and 1/8 teaspoon almond extract for this recipe.)
• Don’t bake blondies until the center is set. They’re done when they still look a touch doughy in the center because they will continue cooking in the pan.
• The frosting is optional. Yes, the frosting is delicious and it whips up in just minutes. And yes, it completes the birthday cake look. But it really is gilding the lily; these blondies are amazing even without frosting!

Blondie Bar Cookies FAQs

What is a Bar Cookie?

I’ve heard this dessert called a blondie cake, but that’s a little misleading because blondes have a very different texture than cake. They’re a bar cookie!

A bar cookie is essentially made from cookie dough that’s pressed into a pan, baked, and then cut into bars.

Bar cookies taste similar to regular cookies. However, the texture is quite a bit different; bar cookies are a bit chewier and gooier than regular cookies.

This is because bar cookies are baked as one big unit and then cut. As a result, only the bar cookies that are cut from the outside have a crispy edge.

How Do I Know When Blondies Are Done?

Blondies are done when the outer edge is light golden brown. The dough should look set along the outer inch or so of the pan, but it should still look doughy in the center.

Your blondies will continue cooking in the hot pan even after you take them out of the oven. If you let them bake until they don’t look doughy in the center, they will be dry and not gooey.

I don’t recommend a toothpick test for blondies because if the toothpick comes out dry, your blondies will be overcooked!

How Are Blondies Different Than Cake?

Blondies are much denser and chewier than cake. Cake is typically light and fluffy because of a leavening agent, such as baking powder or baking soda. On the other hand, blondies don’t typically contain a leavening agent like that.

Blondies are meant to be dense and moist instead of light and fluffy.

More Blondies Recipes to Make

• Ballpark Blondies
• Cinnamon Apple Blondies
• Butterbeer Brown Butter Blondies
• Salted Brown Butter Blondies