Birthday Cake Brownies are my go-to when I want fudgy chocolate brownies but also want that classic birthday cake frosting on top. It’s basically a brownie base with a thick layer of vanilla buttercream and rainbow sprinkles everywhere.
The brownie layer is rich and chewy with a deep cocoa flavor, and the frosting is soft, sweet, and fluffy like the stuff you want to swipe from the bowl. I like this combo because it tastes like two desserts at once, and it slices into neat little bars that are easy to serve.
These are especially good for parties and bake sales, or any time you need a birthday dessert bar that doesn’t require stacking cake layers. I also like them for holiday cookie trays when I want something bright and simple.
Why You’ll Love This Recipe
Fudgy brownie base: This recipe gives you set edges with a softer center, which is exactly what I want in a chocolate brownie.
Classic birthday cake topping: The vanilla buttercream frosting makes these taste like a funfetti-style birthday treat, even though the base is all chocolate.
Easy to slice and serve: Chill them briefly and you get clean cuts, tidy bars, and no messy plating.
Great for parties: They travel well, hold up on a dessert table, and the sprinkles make them look finished with almost no effort.
Flexible add-ins: You can go with chocolate chips, swap in white chips, or keep it simple for more of a classic frosted brownie.
Ingredients You’ll Need
Brownies
- Unsalted butter: Melted butter keeps the brownie batter simple and gives you that dense, fudgy texture. I lightly grease the pan too, but parchment matters more.
- Granulated sugar: This gives the brownies that shiny, crinkly top. It also helps the edges set up nicely.
- Light brown sugar: Brown sugar adds a little chew and keeps the brownies from tasting flat. Dark brown sugar works too if that’s what you have.
- Eggs: Room temperature eggs mix in more smoothly, especially since the butter is melted. Cold eggs can make the batter seize a little.
- Vanilla extract: Don’t skip it. It makes the chocolate taste more like “brownie” and less like plain cocoa.
- Unsweetened cocoa powder: I use regular unsweetened cocoa here. If you use Dutch-process, the flavor will be a little deeper and less sharp.
- All-purpose flour: Regular flour is perfect here. Measure it lightly so you don’t end up with dry brownies.
- Fine salt: A small amount keeps the chocolate and frosting from tasting too sweet. If you only have kosher salt, use a little more.
- Baking powder: Just a touch helps the brownies lift a bit so they don’t feel heavy. This is not a cakey brownie, though.
- Semisweet chocolate chips: Optional, but I like them for little pockets of chocolate. White chocolate chips are fun if you want a more “birthday cake brownies” feel.
- Rainbow sprinkles: I strongly prefer jimmies here because they bleed less color into the batter. Save a handful for the top too.
Birthday Cake Frosting
- Unsalted butter: Softened butter is the base of the frosting, so make sure it’s actually soft. If it’s still cool and firm, it won’t get fluffy.
- Powdered sugar: Sifting helps if yours is lumpy. If you skip sifting, just expect to beat it a little longer.
- Milk: This loosens the frosting and makes it spreadable. Add it slowly so it doesn’t get too thin.
- Vanilla extract: This is the “birthday cake” part of the flavor for me, so I use a full splash. Clear vanilla is fine if you like that classic bakery-style look.
- Fine salt: A tiny pinch makes the frosting taste more balanced. It matters more than you’d think.
- Rainbow sprinkles: Sprinkle them on right after frosting so they stick. Again, jimmies bleed less than nonpareils.
Recipe Instructions
- Preheat the oven: Heat the oven to 350°F. Line an 8-inch square pan with parchment paper (leave a little overhang), then lightly grease the parchment and sides.
- Mix the sugars: In a medium bowl, whisk the melted butter with the granulated sugar and brown sugar until the mixture looks glossy.
- Add the eggs: Whisk in the eggs one at a time, mixing well after each one. Stir in the vanilla until combined.
- Mix the dry ingredients: In a separate bowl, whisk the cocoa powder, flour, salt, and baking powder until evenly mixed.
- Add the dry ingredients: Fold the dry mixture into the wet mixture just until you no longer see dry flour. Don’t overmix.
- Fold in the add-ins: Fold in the chocolate chips (if using) and the sprinkles briefly, just until they’re mixed in.
- Bake: Spread the batter evenly in the pan. Bake for 22 to 28 minutes, until the edges are set and a toothpick in the center comes out with a few moist crumbs.
- Cool: Let the brownies cool completely in the pan. They need to be fully cool before you frost them.
- Make the frosting: Beat the softened butter until smooth. Gradually beat in the powdered sugar, salt, vanilla, and milk until fluffy and spreadable, adding a little more milk if needed.
- Frost and finish: Spread the frosting over the cooled brownies and top with sprinkles. Chill for about 15 minutes for cleaner cuts, then slice and serve.
Some of my tips!
This is the part that really makes a difference. If you only read one section, make it this one because this is where I share the little trick that helps the recipe turn out so well.
Recipe Tips & Tricks
Use parchment paper. This is one of those bar recipes where a parchment sling makes life easier. You can lift the whole slab out for frosting and slicing.
Don’t overbake the brownies. The edges should look set, and the center should look just set, not dry. A toothpick should come out with moist crumbs, not clean.
Stick with jimmies for the sprinkles. Nonpareils tend to bleed fast and can turn your batter a weird color. Jimmies usually behave better in both the brownie batter and on top.
Cool completely before frosting. If the brownies are even a little warm, the buttercream will melt and slide around. I give them plenty of time, especially in a warm kitchen.
Chill before slicing. Even a short chill helps the frosting firm up so you get cleaner edges. It also keeps the sprinkles from dragging through the frosting as you cut.
Make some touches!
There are plenty of easy ways to serve this depending on the occasion. Keep it simple, or add a few small touches to make it feel a little more special.
Serving Suggestions
- Milk: A cold glass of milk is classic with these, especially because the frosting is sweet. I like whole milk or chocolate milk here.
- Coffee or espresso: These are really good with coffee, hot or iced. The bitterness plays nicely with the frosting.
- Ice cream: Serve a brownie bar with vanilla ice cream on the side if you want something a little more “birthday dessert” on a plate. A little extra sprinkle on top is fine.
- Fruit: Fresh strawberries or raspberries are nice alongside the brownies. It keeps the plate from feeling too heavy.
Save it for later
This section covers how to store leftovers and what parts of the recipe you can prepare ahead of time.
Storage and Make Ahead
Store leftovers covered in the fridge for up to 4 days. Because of the frosting, I keep these chilled. Let a bar sit out for 10 to 15 minutes if you want a softer bite.
You can make this recipe ahead by baking the brownies a day early and frosting them the next day. I like this approach because the brownie layer is fully cooled and easy to handle.
If you want them to last longer, freeze individual portions in an airtight container. Thaw in the fridge overnight or at room temperature for a bit before serving.
A few quick answers
This section covers a few extra details that may help before you head to the recipe card.
Recipe FAQs
How do I know when the brownies are done?
I look for set edges and a center that looks just set (not jiggly and wet, but not dry either). A toothpick in the middle should come out with a few moist crumbs.
Can I use a 9-inch pan instead of an 8-inch pan?
You can, but the brownies will be thinner and they’ll bake faster. Start checking a few minutes early, and don’t be surprised if the center sets sooner than you’re used to.
Do sprinkles bleed into the batter?
They can, depending on the type. I’ve had the best luck with jimmies since they hold their color better than nonpareils.
Can I skip the chocolate chips or swap them?
Yes. You can leave them out for a more classic funfetti brownie vibe, or swap semisweet chips for white chocolate chips if you want it sweeter and more “birthday cake.”
Can I freeze these after frosting?
Yes, I do it as individual bars so they’re easy to grab. The sprinkles might soften a bit after thawing, but the flavor and texture are still good.
You might also like
Before you go, take a look at a few other recipes below the recipe card. They use similar ingredients in a different way and are worth saving too.
MORE DINNER RECIPES TO TRY
Birthday Cake Brownies
INGREDIENTS
Brownies
- 1/2 cup unsalted butter melted
- 1 cup granulated sugar
- 1/2 cup light brown sugar packed
- 2 large eggs room temperature
- 2 tsp vanilla extract
- 1/2 cup unsweetened cocoa powder
- 3/4 cup all purpose flour
- 1/2 tsp fine salt
- 1/4 tsp baking powder
- 1/2 cup semisweet chocolate chips optional
- 1/3 cup rainbow sprinkles plus more for topping.
Birthday Cake Frosting
- 1/2 cup unsalted butter softened
- 2 cups powdered sugar sifted
- 2 tbsp milk plus more as needed
- 1 1/2 tsp vanilla extract
- pinch of fine salt
- rainbow sprinkles for topping.
INSTRUCTIONS
Bake Brownies
- heat oven to 350 F and line an 8 inch square pan with parchment then lightly grease
- whisk melted butter granulated sugar and brown sugar until glossy
- whisk in eggs one at a time then mix in vanilla
- whisk cocoa powder flour salt and baking powder in a separate bowl then fold into wet batter just until combined
- fold in chocolate chips and sprinkles briefly to avoid overmixing
- spread batter evenly in pan and bake until edges are set and a toothpick inserted in the center comes out with a few moist crumbs 22 to 28 minutes
- cool completely in pan.
Frost And Finish
- beat softened butter until smooth then gradually beat in powdered sugar salt vanilla and milk until fluffy and spreadable adding milk as needed
- spread frosting over fully cooled brownies and top with sprinkles
- chill 15 minutes for cleaner cuts then slice and serve.
