Frosted Funfetti Blondies are a birthday cake blondie recipe that's soft and chewy with buttery vanilla flavor, colorful sprinkles, and gooey marshmallow pockets. Brown sugar creates a rich, chewy texture while vanilla, butter extract, and rainbow jimmies give every bite that classic birthday cake flavor before a layer of creamy frosting finishes them off.
If you enjoy fun dessert bars, you may also like our White Chocolate Raspberry Swirl Blondies or our Snickerdoodle Blondies.
Frosted Funfetti Blondies Recipe at a Glance 🔎
- 🕒 Prep Time: 15 minutes
- ⏱️ Cook Time: 30 minutes
- ⏱️ Cool Time: Until completely cool (about 2 hours)
- 👥 Servings: 9 large blondies (or 16 small squares)
- 🔥 Cook Method: Bake
- 🍽️ Cuisine (or General Category): American Dessert
- 👩🍳 Pair With: Vanilla ice cream, fresh berries, or a cold glass of milk
- ⭐ Difficulty Level: Easy
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We've baked these birthday cake blondies for everything from birthdays to school parties, and they're always even better topped with vanilla buttercream and extra sprinkles. ~Jami
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Why We Love This Recipe
- Soft And Chewy Texture: Brown sugar, melted butter, and an extra egg yolk create dense, chewy blondies with crisp edges and soft centers.
- Classic Birthday Cake Flavor: Vanilla extract, butter extract, and colorful rainbow sprinkles give these bars the nostalgic flavor of birthday cake without using a cake mix.
- Easy One-Bowl Dessert: The batter comes together quickly with simple pantry ingredients, making these blondies perfect for birthdays, bake sales, or weekend baking.
- Perfect For Celebrations: Frosting and sprinkles make these blondies easy to customize for birthdays, holidays, baby showers, or any festive gathering.
Key Ingredients
- Brown Sugar: Brown sugar is what gives these blondies their signature chew. The extra molasses keeps the bars soft for several days and creates a richer flavor than using white sugar alone.
- Melted Butter: Melted butter produces a denser blondie than softened butter. Let it cool slightly before mixing so it doesn't cook the eggs while still blending smoothly with the sugar.
- Vanilla and Butter Extract: Vanilla provides the familiar bakery flavor, while a small amount of butter extract creates that unmistakable birthday cake taste. Together they make these bars taste much more festive than vanilla alone.
- Rainbow Jimmies: Use jimmies rather than nonpareils. Jimmies hold their color during baking, while nonpareils often bleed into the batter and create gray streaks.
- Mini Marshmallows: Mini marshmallows create soft, gooey pockets throughout the blondies. Tossing them with a little flour helps them stay suspended in the batter instead of melting completely away.
- Flour And Baking Powder: Measure the flour correctly using the spoon-and-level method to avoid dry blondies. Baking powder provides just enough lift while keeping the bars dense and chewy.
A full ingredient list with exact measurements can be found in the recipe card below.
Substitutions & Variations
- Butter Extract: If you don't have butter extract, replace it with additional vanilla extract. The blondies will still taste delicious, though they'll have a milder birthday cake flavor.
- Mini Marshmallows: White chocolate chips make a great substitute if you prefer a cleaner slice or don't enjoy gooey marshmallow pockets.
- Rainbow Jimmies: Change the sprinkle colors for holidays, baby showers, graduation parties, or sports team celebrations. Always use jimmies for the best results.
- Presentation: Finish the cooled blondies with vanilla buttercream, extra rainbow sprinkles, and a few pieces of birthday cake candy for a bakery-style appearance.
- Kid-Friendly: Let kids help stir in the sprinkles and decorate the frosted blondies with their favorite colorful toppings.
How To Make Frosted Funfetti Blondies Recipe
STEP ONE: Prepare the Pan and Mix the Wet Ingredients
Preheat the oven to 350°F and line an 8×8-inch metal baking pan with parchment paper, leaving enough overhang to lift the blondies out after baking.
Whisk the melted butter and brown sugar together for about a minute until the mixture looks smooth and glossy. This helps dissolve some of the sugar for that signature shiny, crackly top. Add the egg, egg yolk, vanilla extract, and butter extract, then whisk until completely smooth.
STEP TWO: Fold in the Dry Ingredients
Whisk together the flour, baking powder, and salt in a separate bowl. Add the dry ingredients to the wet mixture and gently fold everything together just until no streaks of flour remain.
Fold in the rainbow jimmies first so they're evenly distributed throughout the batter. Toss the mini marshmallows with a teaspoon of flour, then gently fold them in just until combined.
STEP THREE: Spread the Batter
Spread the batter evenly into the prepared pan. An offset spatula or lightly greased spoon makes this much easier because the batter is thick.
STEP FOUR: Bake, Cool, and Frost
Bake for 28 to 32 minutes, until the edges are lightly golden and set while the center still looks slightly soft. The top should have a shiny, crackly finish. A toothpick inserted near the center should come out with a few moist crumbs instead of wet batter.
Let the blondies cool completely in the pan. Once cooled, spread the frosting evenly over the top and finish with more rainbow sprinkles before slicing into squares.
Expert Tips for Success
👩🍳Jami's Pro Tips: Want to take this recipe to the next level? Check out my expert tips below for the best flavor, texture, and meal prep hacks!
✔️ DO Mix the batter only until the flour disappears.
✔️ DO Let the butter cool down before adding the eggs.
✔️ DO Let the blondies cool completely before frosting for the cleanest finish.
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Storage
Store frosted blondies in an airtight container at room temperature for up to 3 days or refrigerate for up to 1 week. For longer storage, freeze unfrosted blondies in a freezer-safe container for up to 3 months. Thaw overnight in the refrigerator or at room temperature, then frost before serving for the freshest flavor and texture.
Frosted Funfetti Blondies Recipe FAQs
Birthday cake blondies have the same buttery, chewy base as classic blondies but include rainbow sprinkles and vanilla-forward flavoring for that nostalgic birthday cake taste. Many versions, including this one, are finished with vanilla buttercream for an extra festive dessert.
Too much flour, overmixing, or overbaking are the most common causes. Measure the flour carefully, stir only until combined, and remove the blondies while the center still looks slightly soft. They continue to firm up as they cool.
Use rainbow jimmies instead of nonpareils. Jimmies hold their shape and color during baking, while nonpareils often dissolve and create gray or muddy streaks.
The edges should be lightly golden and set, while the center should still look slightly underbaked. A toothpick inserted near the center should come out with a few moist crumbs but no raw batter. Overbaking is the fastest way to lose that soft, chewy texture.
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📖 Recipe
Frosted Funfetti Blondies
Equipment
- 8×8-inch metal baking pan
- Parchment paper
- Large Mixing Bowl
- Medium mixing bowl
- Whisk
- Rubber spatula
- Wire cooling rack
- Offset spatula or butter knife (for spreading the frosting)
Ingredients
Blondies
- ¾ cup unsalted butter melted and slightly cooled
- 1¼ cups packed light brown sugar
- 1 large egg room temperature
- 1 large egg yolk room temperature
- 1 tablespoon pure vanilla extract or 1 teaspoon vanilla extract plus ½ teaspoon butter extract
- 1¾ cups all-purpose flour
- 1 teaspoon baking powder
- ½ teaspoon salt
- ½ cup rainbow jimmies plus more for topping
- ¾ cup mini marshmallows tossed with 1 teaspoon flour
Vanilla Buttercream
- ½ cup unsalted butter softened
- 2 cups powdered sugar
- 2 tablespoons heavy cream or whole milk
- 1 teaspoon vanilla extract
- ¼ teaspoon butter extract optional
- pinch salt
- rainbow jimmies for decorating
Instructions
- Preheat the oven to 350°F (177°C). Line an 8×8-inch metal baking pan with parchment paper, leaving enough overhang to lift the blondies out after baking.
- Whisk the melted butter and brown sugar together until smooth and glossy, about 1 minute.
- Add the egg, egg yolk, vanilla extract, and butter extract (if using). Whisk until completely combined.
- In a separate bowl, whisk together the flour, baking powder, and salt. Fold the dry ingredients into the wet ingredients just until combined. Do not overmix.
- Fold in the rainbow jimmies, then gently fold in the floured mini marshmallows. Spread the thick batter evenly into the prepared pan.
- Bake for 28 to 32 minutes, or until the edges are lightly golden and set while the center still looks slightly soft. The top should have a shiny, crackly finish, and a toothpick inserted near the center should come out with a few moist crumbs but no wet batter.
- Let the blondies cool completely in the pan on a wire rack.
Make the Icing
- While the blondies cool, beat the softened butter until creamy.
- Gradually mix in the powdered sugar, then beat in the heavy cream, vanilla extract, butter extract (if using), and salt until light and fluffy. If needed, adjust the consistency with a little more cream or powdered sugar.
- Spread the buttercream evenly over the blondies using an offset spatula or the back of a spoon. Immediately sprinkle the top with additional rainbow jimmies.
- Allow the frosting to stand at room temperature for at least 20 to 30 minutes before slicing.
- For clean, bakery-style squares, refrigerate the frosted blondies for 30 to 45 minutes before slicing. Run a sharp knife under hot water, wipe it dry, and slice in one smooth motion, cleaning the knife between cuts as needed.
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Notes
- Use rainbow jimmies instead of nonpareils to keep the colors bright.
- Mix the batter only until the flour disappears for the softest blondies.
- Toss the marshmallows with a little flour so they stay evenly distributed.
- Wait until the blondies are completely cool before adding the frosting.
Jami Powell says
A fun and unique way to celebrate a birthday without a traditional cake!