Homemade Cosmic Brownies Recipe

Name: Homemade Cosmic Brownies
Prep time: 10 min
Cook time: 20 min
Total time: 30 min
Yield: 24
Ingredients: 3/4 cup butter, unsalted, melted; 1 cup granulated sugar; 2/3 cup brown sugar, packed; 2 teaspoons vanilla; 2 eggs, room temp; 1 1/4 cups flour; 3/4 cup unsweetened cocoa powder; 1/2 teaspoon baking powder; 1 Tablespoon cornstarch; 1 pinch salt; 3 Tablespoons milk; 3/4 cup heavy whipping cream; 1 cup semi sweet chocolate chips; 2 small bags Rainbow Chips

By:

Josie Baker

Published:

October 1, 2026

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Homemade Cosmic Brownies

Homemade cosmic brownies capture everything you loved about the lunchbox classic, baked fresh in your own kitchen. The base is a thick and chewy chocolate brownie, and the top is a glossy fudge ganache covered with rainbow chips.

You only need pantry basics and one baking pan, and the whole thing comes together in about half an hour. Bring them to birthday parties, school bake sales, or a quiet Sunday afternoon with a cold glass of milk.

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Copycat Cosmic Brownies Recipe

This is a copycat version of the Little Debbie Cosmic Brownies I grew up with. My mom tucked one into my lunch bag almost every week, and I would eat the corner first before the bus even pulled away from the curb.

That little square of chocolate was the best part of the day, and I still think about it whenever I smell cocoa powder.

Here is the detail that matters in my house: this homemade version skips the nuts. The original brownies with nuts were never my favorite, so I always reached for the one covered in rainbow chips instead. If your kids are particular about texture the way mine are, that one change makes this recipe a keeper.

These brownies are also a nostalgic treat for parties. They look just like the ones from the store, so guests recognize them right away, but the flavor runs deeper because you are using real melted butter, two kinds of sugar, and a ganache made from heavy cream and chocolate chips.

Homemade Cosmic Brownies, Copycat Cosmic Brownies Recipe

That is the difference between a brownie that vanishes off the plate and one that sits there until you throw it away.

Be sure to read the recipe through once before you start. It moves quickly, and having everything on the counter makes the whole process feel simple and relaxed.

If nuts in brownies are not your thing, this is the version for you. Fudge ganache below, rainbow chips on top, and no crunch getting in the way.

Ingredients

For your convenience, I grouped everything so you can set it out on the counter before the oven goes on. Nothing here is hard to find, and most of it is already sitting in your pantry.

For the Brownies:

3/4 cup unsalted butter, melted
1 cup granulated sugar
2/3 cup brown sugar, packed
2 teaspoons vanilla
2 eggs, room temperature
1 1/4 cups flour
3/4 cup unsweetened cocoa powder
1/2 teaspoon baking powder
1 Tablespoon cornstarch
1 pinch of salt
3 Tablespoons milk

For the Frosting:

3/4 cup heavy whipping cream
1 cup semi sweet chocolate chips
2 small bags of Rainbow Chips

Kitchen Tools Used:

The equipment is basic, which is part of why I make these so often.

Non slip mixing bowls
A medium saucepan
A wire whisk
A 9×13 inch baking pan
Parchment paper

Instructions

Set your oven rack in the middle and give yourself a clear workspace. The batter comes together quickly, so the steps below read faster than you might expect.

Brownie Directions:

Get the oven and pan ready. Preheat the oven to 350 degrees Fahrenheit and line a 9×13 inch baking dish with parchment paper. Mist the paper with baking spray and set the pan aside.
Beat the butter, sugars, and vanilla. In a large bowl, beat the melted butter, granulated sugar, brown sugar, and vanilla with an electric mixer or a stand mixer until the mixture looks smooth and glossy.
Add the eggs one at a time. Crack in the eggs one at a time, mixing after each addition until each egg is fully incorporated. Take your time here, because the eggs are what pull the batter together.
Whisk the dry ingredients. In a separate mixing bowl, whisk together the flour, unsweetened cocoa powder, baking powder, cornstarch, and salt until there are no cocoa lumps left.
Combine the wet and dry mixtures. Gradually add the flour mixture to your batter, mixing on low speed. Alternate adding flour and milk until everything is combined. Your batter should be fairly thick, and that is exactly what you want.
Spread it in the pan. Scoop the batter into the prepared baking pan and spread it with a spatula as evenly as possible, pushing it into the corners.
Bake. Bake at 350 degrees Fahrenheit for 18 to 25 minutes, taking care not to overcook. Set a timer for 18 minutes and check from there, because a chewy brownie is far better than a dry one.
Cool in the pan. Remove the brownies from the oven and allow them to cool completely in the pan before you frost them.

Frosting Directions:

Heat the heavy whipping cream in a saucepan until it starts to simmer. Watch it closely, because you want a gentle simmer rather than a rolling boil. Remove it from the heat and add the semi sweet chocolate chips.
Let the chips sit in the hot cream for a couple of minutes, then whisk until the mixture is melted and completely smooth.
Pour the ganache over the top of the cooled brownies and smooth it with a spatula, working it out toward the edges.
Sprinkle the rainbow chips over the top while the frosting is still wet so they stay put once it sets.
Allow the frosting to set, then slice and enjoy.

Prep Tips

These brownies work in either of two pans, and the pan you choose changes the final texture. A 9×13 inch rectangle gives you thinner brownies that taste a lot like the store bought ones, which is what I usually reach for.

A 9×9 inch square pan gives you thicker brownies, and those may need a couple of extra minutes in the oven.

Be sure to test for doneness with a toothpick. Insert it near the center, and if it comes out with a few moist crumbs instead of wet batter, the brownies are ready to come out.

Let them cool completely before the ganache goes on, or the frosting will slide around the pan. If you want tidy slices, run your knife under warm water and wipe it dry between cuts.

In our house, any leftovers go into a covered container on the counter, and they never last longer than a day or two.

Cosmic Brownies Recipe (Printable Recipe Card):

The printable recipe card below keeps everything in one place, so you can cook straight from your phone or print a copy for the recipe box. If you make these brownies, I would love it if you rated the recipe and shared your thoughts in the comments.

Be sure to pin our cosmic brownie recipe on Pinterest:

Save it to your dessert board so you can find it the next time a craving hits.

Ingredients

Here is the full ingredient list one more time, laid out for a quick grocery run or a screenshot on your phone.

Ingredient	Amount	Note
Unsalted butter	3/4 cup	melted
Granulated sugar	1 cup
Brown sugar	2/3 cup	packed
Vanilla	2 teaspoons
Eggs	2	room temperature
Flour	1 1/4 cups
Unsweetened cocoa powder	3/4 cup
Baking powder	1/2 teaspoon
Cornstarch	1 Tablespoon
Salt	1 pinch
Milk	3 Tablespoons
Heavy whipping cream	3/4 cup	for the frosting
Semi sweet chocolate chips	1 cup	for the frosting
Rainbow Chips	2 small bags	for the topping

Instructions

This is the short version for the card, from the first step to the last.

Preheat the oven to 350 degrees Fahrenheit and line a 9×13 inch baking dish with parchment paper. Mist it with baking spray and set it aside.
Beat the melted butter, both sugars, and the vanilla in a large bowl using an electric mixer or a stand mixer.
Add the eggs one at a time, mixing until each one is well incorporated.
In a separate bowl, whisk the flour, cocoa powder, baking powder, cornstarch, and salt together.
Gradually add the flour mixture to the batter on low speed, alternating with the milk, until a fairly thick batter forms.
Scoop the batter into the prepared pan and spread it evenly with a spatula.
Bake at 350 degrees Fahrenheit for 18 to 25 minutes, taking care not to overcook, then cool completely in the pan.
For the frosting, heat the heavy whipping cream until it simmers, then remove it from the heat and add the chocolate chips.
Let the chips sit for a couple of minutes, then whisk until the ganache is melted and smooth.
Pour the ganache over the cooled brownies and smooth it with a spatula.
Sprinkle the rainbow chips over the top while the frosting is still wet.
Let the frosting set, then slice and serve.

Notes

The nutrition information below is a rough estimate. Your actual numbers depend on the exact brands and amounts you use, so treat it as a helpful guide rather than a precise measurement.

Per serving	Amount
Calories	214
Carbohydrates	25g
Protein	2g
Fat	12g
Saturated fat	7g
Cholesterol	40mg
Sodium	63mg
Fiber	2g
Sugar	17g

One more note on the pan: a 9×13 inch rectangle gives thinner brownies that look like the store bought version, while a 9×9 inch square pan gives thicker brownies that may need a couple of extra minutes of baking. Either way, use a toothpick to check doneness before you pull them out of the oven.

I also like to let the pan sit at room temperature until the ganache firms up before slicing. It makes the squares look neat on a platter, and the rainbow chips stay in place instead of sliding off.

Recipe details

Here is the quick rundown if you are planning your baking around a busy schedule.

Detail	Time or Amount
Prep time	10 minutes
Cook time	20 minutes
Total time	30 minutes
Servings	24

Slice the pan into 24 squares and serve them straight from the parchment paper, or stack them on a plate for a party. Either way, they are the first thing to disappear from the dessert table.

FAQs

What makes cosmic brownies different from regular brownies?

Cosmic brownies are a copycat version of the classic Little Debbie snack cake, known for their fudgy texture and signature chocolate ganache topping covered in rainbow chip sprinkles. Unlike a traditional brownie, they are baked in a 9×13 inch pan for a thinner, snack-cake-like bar and are made with a combination of granulated and brown sugar for moisture. The recipe includes cornstarch to create a tender, soft crumb that replicates the commercial texture.

How do you make the chocolate ganache for cosmic brownies?

To make the chocolate ganache, heat 3/4 cup of heavy whipping cream in a saucepan until it begins to simmer, then remove it from the heat. Add 1 cup of semi-sweet chocolate chips and let them sit for a couple minutes before whisking until the mixture is melted and smooth. Pour the warm ganache over the cooled brownies and spread it evenly with a spatula.

Can you freeze homemade cosmic brownies?

Yes, you can freeze homemade cosmic brownies for up to three months. For best results, wrap individual slices tightly in plastic wrap and then foil before placing them in a freezer-safe container. Thaw the brownies at room temperature before serving, and the texture will remain fudgy.

What is the best pan size for making cosmic brownies?

A 9×13 inch baking dish is the best pan size for this recipe, as it yields thinner brownies that resemble the original Little Debbie snack cakes. If you use a 9-inch square pan, the brownies will be thicker and more cake-like. The recipe is designed for a 9×13 pan and bakes at 350°F for 18 to 25 minutes.

Homemade Cosmic Brownies Recipe

Homemade Cosmic Brownies

Copycat Cosmic Brownies Recipe