These homemade Cosmic Brownies feature ultra fudgy brownies topped with a simple chocolate ganache frosting and candy-coated chocolate chips. Just like your favorite store-bought brownies, but better!

Two rows of sliced homemade Cosmic Brownies, with one brownie tipped up onto the others.

As a kid, there was no better feeling than opening up your lunchbox to discover that Mom had snuck a Cosmic Brownie in as a treat. The dense, fudgy brownie topped with chocolate frosting and rainbow chocolate chips hit the spot every time! 

Although I have fond memories of digging into those store-bought brownies, I’d much rather enjoy homemade sweet treats these days.

Enter: these homemade Cosmic Brownies. They’re even richer and fudgier than my classic brownies, and they’re topped with an easy three-ingredient chocolate ganache frosting. 

Although this Cosmic Brownie recipe has a few extra steps to it, the process is as straightforward as making regular brownies. You will have to be patient though, as the frosting needs to chill in the fridge for an hour or two to set up!

An overhead view of the ingredients needed to make fudgy brownies with chocolate frosting.

Recipe Ingredients 

This Cosmic brownie recipe has three components: a dense brownie base, a fudge frosting for the brownies, and the rainbow candy-coated chocolate chips. Let’s go over a few important ingredients you’ll need to make this childhood favorite at home. 

  • Butter: I prefer using unsalted butter when baking since the amount of salt in salted butters varies between brands. If you only have salted butter on hand, just omit the salt or reduce it to a tiny pinch.
  • Granulated Sugar & Brown Sugar: In my classic brownie recipe, I only use granulated sugar. But for this recipe, you will be using a mix of granulated and brown sugar. Just 1/2 cup of brown sugar adds moisture and flavor to the brownies, giving them that classic Cosmic Brownie texture and taste.
  • Eggs: You’ll need three whole eggs and one egg yolk to make this recipe. The extra egg yolk adds more fat so that the brownies are super dense and fudgy. Make sure your eggs are at room temperature before whisking them into the batter.
  • Cocoa Powder: The brownies are made solely with cocoa powder and no melted chocolate. You can use either unsweetened natural cocoa powder or Dutch-process cocoa powder. 
  • Semi-sweet Chocolate: I recommend chopping two 4-ounce bars of chocolate and melting them to make the fudge frosting rather than use chocolate chips, which contain stabilizers and are more resistant to melting. 
  • Corn Syrup: This ingredient is optional, but it makes the chocolate brownie frosting glossy. If you don’t have any on hand, you may omit it.
  • Cosmic Brownie Sprinkles: I used rainbow candy-coated chocolate chips on top of the ganache frosting. You can find them at Walmart, on Amazon, or you can substitute them with mini M&M’s or regular sprinkles.

How to Make Cosmic Brownies 

Making copycat Cosmic Brownies at home couldn’t be simpler! First, you’ll need to make the fudgy brownies. 

  • Whisk together the wet ingredients: In a large bowl, whisk together the melted butter and sugars. Then, whisk in the eggs, egg yolk, and vanilla. 
  • Add the dry ingredients: The dry ingredients can be added directly to the wet mixture. I recommend sifting them into the mixing bowl to ensure there are no lumps in the batter. 
  • Bake the brownies: Pour the batter into a parchment paper or foil-lined 9×13-inch baking dish. Bake until a toothpick inserted in the center comes out clean, but with a few moist crumbs. 

An overhead view of sliced cosmic brownies. A small metal measuring up with rainbow chips is beside the brownies.

After the brownies come out of the oven, you must let them cool completely before topping them with the chocolate ganache frosting.

  • Add the chopped chocolate and corn syrup to a bowl: Set this aside while you heat the heavy cream.
  • Heat the heavy cream: You can do this on the stove over medium-low heat, or you can heat the cream in the microwave. 
  • Pour the cream over the chopped chocolate: Pour the simmering cream over the chopped chocolate and corn syrup and let rest for 3 minutes before whisking it all together. If all of the chocolate has not melted, microwave the mixture in 20-second increments until it’s smooth.
  • Frost the brownies: Smooth the ganache frosting over the cooled brownies, then sprinkle with candy-coated chocolate chips. 
  • Chill the brownies: The frosting needs time to firm up in the fridge, about 1 to 2 hours. If you try to cut the brownies right away, the frosting will ooze all over the pan and you won’t have perfect homemade Cosmic Brownies. 

An angled view of cosmic brownies. One is stacked on another and has a bite taken out of it.

Storage Instructions 

The ganache will soften at room temperature, so it’s best to keep these brownies refrigerated. Cover the pan with plastic wrap, or transfer the brownies to an airtight container. They’ll last up to five days in the fridge. 

Can This Recipe Be Made in Advance? 

Yes, you can bake the brownies a day in advance and frost them the day you plan on serving them. Or, prepare the entire Cosmic Brownie recipe as written up to 24 hours before slicing and serving. The brownies keep well in the fridge, tightly covered. 

Can Mix-Ins Be Added to the Batter? 

Absolutely! Store-bought Cosmic Brownies don’t contain any mix-ins so I didn’t use any in this recipe. However, mini chocolate chips or finely chopped nuts would be delicious in these brownies. I suggest only using about 1 cup of mix-ins if you do add them.

A stack of three homemade Cosmic Brownies. The top brownie is missing a bite.

Baking Tips 

  • I recommend lining your pan with foil or parchment paper and leaving some overhang. This will make it much easier to remove the brownies from the pan!
  • Room temperature eggs will mix much easier into the batter. If you forget to set them out ahead of time, place them in a bowl of warm water for 5 to 10 minutes.
  • The corn syrup in the chocolate brownie frosting is optional, but recommended. It makes the frosting glossy and gives the brownies a store-bought appearance. 
  • You MUST let the brownies cool completely before frosting them. If needed, you can make the brownie base in advance, then frost them later on when you have time.
  • Want to freeze these brownies? Slice the chilled brownies, wrap each one tightly with plastic wrap, and store them in a large freezer bag/container for up to 3 months. When you’re ready to enjoy them, thaw overnight in the refrigerator. 

More Easy Brownie Recipes to Make! 

Recipe Video

If you want to see a full video tutorial on how these brownies are made, you can watch the video below!

Several cosmic brownies sliced on a piece of parchment paper. One brownie has a bite taken out and is sitting on top of another brownie.

Homemade Cosmic Brownies

5 from 8 ratings
Prep Time: 30 minutes
Cook Time: 30 minutes
Chill Time: 2 hours
Total Time: 3 hours
These homemade Cosmic Brownies feature ultra fudgy brownies topped with a simple chocolate ganache frosting and candy-coated chocolate chips. Just like your favorite store-bought brownies, but better!


Servings: 24 brownies

For the Brownies:

  • 1 cup unsalted butter melted and slightly cooled (2 sticks, 230 grams)
  • 1 ¾ cups granulated sugar (350 grams)
  • ½ cup packed light brown sugar (100 grams)
  • 3 large eggs at room temperature
  • 1 large egg yolk at room temperature
  • 1 teaspoon pure vanilla extract
  • 1 cup unsweetened cocoa powder (90 grams)
  • 1 cup all-purpose flour spooned & leveled (125 grams)
  • ½ teaspoon salt

For the Ganache:

  • 8 ounces semisweet chocolate finely chopped (226 grams)
  • 1 tablespoon light corn syrup optional but adds glossiness (20 grams)
  • ½ cup heavy cream (120 ml)

For the topping:

  • Rainbow candy coated chocolate chips, mini m&m's, or sprinkles


  • To make the brownies: Preheat the oven to 350°F (180°C). Line a 9x13-inch baking pan with foil or parchment paper, making sure to leave some overhang for easy removal. If using foil, spray it well with nonstick cooking spray, and set aside.
  • In a large mixing bowl, whisk together the melted butter, granulated sugar, and brown sugar until well combined. Then whisk in the eggs, egg yolk, and vanilla extract until fully combined.
  • Sift in the cocoa powder, flour, and salt and continue whisking until just combined, stopping to scrape down the sides of the bowl as needed.
  • Scoop the batter into the prepared baking pan and spread it around into one even layer. Bake for 27 to 33 minutes or until a toothpick inserted into the center comes out clean with just a few moist crumbs.
  • Remove from the oven and allow to cool completely.
  • To make the ganache: Place the chopped chocolate and corn syrup into a large heatproof bowl. Set aside.
  • Heat the heavy cream in a medium pot and bring to a simmer on the stove (or heat in the microwave for 45 seconds to 1 minute).
  • Pour the simmering cream over the chocolate and let it sit for 3 minutes.
  • Mix with a rubber spatula or spoon until the mixture is smooth and well combined. If any chocolate clumps remain, microwave in 20 to 30-second increments until melted and smooth.
  • Use a spatula or spoon to spread the chocolate ganache over the cooled brownies.
  • Sprinkle with rainbow candy coated chocolate chips, mini M&Ms, or sprinkles. Refrigerate for 1 to 2 hours to allow the ganache to set before serving. Cut into squares when ready to serve!


Storage Instructions: Brownies may be stored in an airtight container in the refrigerator for up to 5 days.
Freezing Instructions: Slice the chilled brownies, wrap each one tightly with plastic wrap, and store in a large freezer bag/container for up to 3 months. Thaw overnight in the refrigerator. 
Cuisine: American
Course: Dessert
Author: Danielle
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