Brownie Birthday Cake

This Brownie Birthday Cake recipe is made with thick, fudgy, and gooey brownies from a box mix layered between homemade vanilla buttercream frosting and rainbow sprinkles. A delicious alternative to a classic birthday cake recipe: a birthday cake from brownie mix!

Birthday Cake From Brownie Mix

I grew up on brownies from a box mix and I’m here to say they are sooo underrated.

Aside from being so fudgy and delicious, you only need four ingredients – which you probably already have at home.

Also, they are a no-brainer; simply mix the ingredients together, pour the batter in a ‘properly greased’ (see instructions below) baking pan, and pop them in the oven.

Brownie Cake Frosting

Frosting, on the other hand, is a little different.

I love a classic homemade buttercream frosting.

Don’t get me wrong, I’ll certainly use frosting containers from the grocery store in a pinch, or if the recipe is relatively time-consuming (like my American Flag Brownies).

However, there is something about a classic buttercream that just cannot be topped…

And this is how we have ended up with this Brownie Birthday Cake recipe made with box-mix brownies and homemade buttercream frosting.

Lastly, before we jump into the details, if you’re wondering about the sprinkle cookies around the cake, you can check them out here.

Brownie Birthday Cake Recipe

In this post, we will cover:

• Ingredients
• Equipment
• Instructions
• Video
• Notes
• Recipe Card

Brownie Birthday Cake Ingredients

Brownies Ingredients

1. Brownie mix: I used two boxes of the Ghirardelli Double Chocolate Brownie Mix, which were easy and so delicious.
2. Eggs: Generally, one mix calls for one large egg, but be sure to double-check the box, if you don’t use the Ghirardelli brand.
3. Half-and-half: Most brownie mix recipes call for water, but I like to swap in dairy for extra richness.
4. Oil: Most recipes call for vegetable oil, but I’ve used canola oil, in a pinch, when I was out of veggie oil, and the brownies still tasted delicious.
5. Shortening: I generally won’t include shortening or spray butter in ingredient lists, but it is SO important that you use shortening for this recipe so that you can easily remove your baked brownies from the pan.

Buttercream Frosting Ingredients

1. Confectioners sugar: to make the frosting sweet.
2. Unsalted butter (super-soft): you could also use salted butter and omit the added table salt.
3. Salt: to balance out the sweetness from the sugar.

The reason this frosting recipe doesn’t call for liquid, such as milk, is because you are using super-soft butter and we are going for a thick and rich buttercream frosting.

If leaving your butter on the counter at room temperature isn’t enough to make the butter super-soft, then set it on top of the oven while it is preheating. Just make sure you keep an eye on it so that it doesn’t melt.

I do not recommend microwaving the butter. I promise it is worth the wait!

If you feel that it’s not getting to the super-soft consistency, you can add a 1/2 tablespoon to 1 tablespoon of milk, half and half, or heavy cream when you are beating the butter in the mixer.

Brownie Birthday Cake Equipment

In addition to getting all my ingredients out before baking, I like to get all my equipment out, too. Here’s what you’ll need for this recipe:

1. Stand mixer or (hand mixer + mixing bowl) to mix the brownie ingredients and the frosting ingredients.
2. Spatula: to scrape brownie batter and frosting from the side of the bowl, and transfer it out of the bowl.
3. Measuring cups: to measure the brownie and frosting ingredients.
4. 8″ round cake pans: to bake the brownies.
5. Parchment paper: to cover the 8″ round cake pans.
6. Scissors: to cut the parchment paper into +8″ round pieces, and to cut the piping bag tip.
7. Piping bag: to frost the brownie cake.
8. Cake turntable: to easily turn the brownie as you frost it.

How To Make A Brownie Birthday Cake Recipe

There are four main steps for this recipe, which are detailed below this section. Click a link to jump to the details (or just keep scrolling):

1. Prepare the Baking Pans
2. Bake The Brownies
3. Make The Buttercream Frosting
4. Frost The Brownie Birthday Cake

For a printable summary of this recipe, jump to the recipe card below.

1. Prepare The Baking Pans

Using a pencil, trace the bottom of an 8″ round cake pan on a piece of parchment paper three times.

Cut out the three circles, leaving about an extra inch of room around the circle (this will make it easier to remove the baked brownies from the pan).

Grease the inside of the cake pans using shortening (not butter spray).

Place a piece of parchment paper in the bottom of each greased pan (make sure the side with the pencil markings is face down).

2. Bake The Brownies

If you are using brownie box mixes like me, simply prepare two boxes according to the package instructions, with the following adjustments:

1. Use half-and-half (or milk) instead of water.
2. Divide the brownie batter across three 8″ baking pans.
3. Bake for 23-25 minutes (you can bake up to two pans at a time).

Let the baked brownies cool completely in the pans on top of a wire rack. Once cooled, remove the brownies from the pan:

1. Carefully insert the end of a rubber spatula between the brownies and the pan, to help loosen the brownies.
2. Pinch a section of the parchment paper, and lift it up just enough to slide your other hand underneath the brownie to lift it out of the pan and place it on a flat surface (like a cutting board).
   • I recommend leaving the parchment paper on the brownie until after you have transferred it to your cake turntable because it’s easier to work with.

3. Make The Buttercream Frosting

Beat the super-soft butter until it is extra creamy, for about a minute or two, using a hand mixer or stand mixer.

Add the salt and about half of the confectioner’s sugar and mix to incorporate.

Scrape the sides and add the remaining confectioner’s sugar and mix until the frosting is light and fluffy for about two to four minutes.

Transfer the icing to a large piping bag using a spatula.

Using scissors, cut the end of the piping bag once you are ready to begin frosting the cake.

4. Frost The Brownie Birthday Cake

Place one of the brownies faced up on a cake decorating turntable.

Hold the piping bag with frosting in your dominant hand and frost the top of the brownie. Then add rainbow sprinkles.

Place a second brownie faced down on top of the icing. Frost the top of the brownie and add rainbow sprinkles.

Repeat this step with the last brownie.

Lastly, frost the side of the brownie cake and add rainbow sprinkles.

Brownie Birthday Cake Recipe Notes

• Your cake will stay fresh for 2-3 days.
• You can leave it on the counter or in the fridge.
• Once you cut a slice, make sure you cover the inside of the cake with plastic wrap so that it doesn’t dry out.
• Take your time removing the brownies from the pan; it’s not difficult to accidentally break the brownie in half if you aren’t careful.

Other Sweet Birthday Recipes

I Want To Hear From You!

Let me know if you have any questions or comments below.

Also, if you made this brownie cake recipe, I’d love to see it! Just tag me on Instagram: @lifestyledbysam_

Brownie Birthday Cake

This Brownie Birthday Cake recipe is made with thick, fudgy, and gooey brownies from a box mix layered between homemade vanilla buttercream frosting and rainbow sprinkles. A delicious alternative to a classic birthday cake recipe: a birthday cake from brownie mix!

Print Recipe Pin Recipe

Prep Time 35 minutes mins

Cook Time 50 minutes mins

Total Time 1 hour hr 50 minutes mins

Course Dessert

Cuisine American

Servings 8 people

Equipment

• Stand mixer (or hand mixer + mixing bowl)
• Spatula
• Measuring cups
• 8" round cake pans
• Parchment paper
• Scissors
• Piping bag
• Cake turntable

Ingredients

  

Brownies

• 2 boxes Brownie mix and brownie mix ingredients
• Half-and-half* swap for water in brownie mix
• Shortening to grease the pan

Buttercream Frosting

• 7 cups Confectioner's sugar
• 2 cups Butter unsalted, extra soft*
• 1 and 1/2 tsp Salt

Instructions

 

• Preheat the oven to 325 degrees.

Prepare The Baking Pans

• Using a pencil, trace the bottom of an 8" round cake pan on a piece of parchment paper three times.
• Cut out the three circles, leaving about an extra inch of room around the circle (this will make it easier to remove the baked brownies from the pan).
• Grease the inside of the cake pans using shortening.
• Place a piece of parchment paper in the bottom of each greased pan (make sure the side with the pencil markings is face down).

Bake The Brownies

• Prepare the brownie box mixes according to the package instructions, with the following two adjustments:
• Use half-and-half instead of water
• Divide the brownie batter across three 8" baking pans.
• Bake for 23-25 minutes (you can bake up to two pans at a time).
• Let the baked brownies cool completely in the pans on top of a wire rack. 
• Carefully insert the end of a rubber spatula between the brownies and the pan, to help loosen the brownies.
• Pinch a section of the parchment paper, and lift it up just enough to slide your other hand underneath the brownie to lift it out of the pan and place it on a flat surface (like a cutting board).

Make The Buttercream Frosting

• Beat the super-soft butter until it is extra creamy, for about a minute or two, using a hand mixer or stand mixer.
• Add the salt and about half of the confectioner's sugar and mix to incorporate. 
• Scrape the sides and add the remaining confectioner's sugar and mix until the frosting is light and fluffy for about 2 - 4 minutes. 
• Transfer the icing to a large piping bag using a spatula. 
• Using scissors, cut the end of the piping bag once you are ready to begin frosting the cake.

Frost The Brownie Birthday Cake

• Place one of the brownies faced up on a cake decorating turntable. 
• Hold the piping bag with frosting in your dominant hand and frost the top of the brownie. Then add rainbow sprinkles.
• Place a second brownie faced down on top of the icing. Frost the top of the brownie and add rainbow sprinkles.
• Repeat this step with the last brownie. 
• Lightly frost the side of the brownie cake and add rainbow sprinkles.

Notes

Cook time assumes you cook two pans at once (23-25 minutes), and cook the third pan by itself (23-25 minutes), for a total of 50 minutes.

* Amount depends on the brownie mix instructions.

** If leaving your butter at room temperature doesn't do the trick, I like to set my on the oven while it is preheating. Just make sure you keep an eye on it so that it doesn't melt. I do not recommend microwaving the butter. I promise it is worth the wait! If you feel that it's not getting to the super-soft consistency, you can add a 1/2 tablespoon to 1 tablespoon of milk, half and half, or heavy cream when you are beating the butter in the mixer.

Keyword Brownies, Cake