Easy-to-make homemade cosmic brownies are rich and fudgy, a classic old fashioned brownie with frosting. The brownies are made in one pot with melted chocolate and then frosted with a creamy chocolate frosting. If you like Cosmic brownies, you’re going to love these frosted brownies.
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These homemade cosmic brownies capture all the magic of your childhood favorite while elevating them to a new level of yummy. With a perfect fudgy texture and that signature glossy chocolate frosting topped with colorful sprinkles, these brownies are guaranteed to bring back memories — and create new ones!
This recipe came to life after countless requests from readers asking for a homemade version of their favorite childhood treat. After weeks of testing and tweaking, I’m thrilled to share this perfected recipe that captures everything we love about cosmic brownies — from the dense, fudgy base to that impossibly smooth chocolate topping.
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Why You’ll Love This Homemade Cosmic Brownie Recipe
- One-Pot Wonder: Both the brownies and frosting are made in a single pot on the stovetop, meaning minimal cleanup and maximum efficiency.
- Better Than Store-Bought: Unlike packaged cosmic brownies, you’re using real, high-quality chocolate and pure vanilla extract. The result is a richer, more complex chocolate flavor that’s worlds apart from the artificial taste of commercial versions.
- Perfect Make-Ahead Dessert: These brownies actually get better after a day in an airtight container, as the flavors deepen and the frosting sets to the perfect consistency. This makes them ideal for preparing in advance for parties, bake sales, or potlucks.
- Big Crowd Pleaser: While these brownies capture the nostalgic memories of the cosmic brownies from your childhood, they’re made with better ingredients and (I think) a more sophisticated taste. Adults and kids all love these brownies!
🍽️ My kids absolutely love it when I surprise them with a homemade brownie snack. It makes the afternoon super special!
Recipe Ingredients
For the Brownies:
- Unsweetened chocolate
- Butter
- Sugar — Granulated and powdered
- Eggs
- Milk
- Vanilla
- All-purpose flour
- Baking powder
- Salt
- Optional additions — sprinkles or chopped nuts
See the recipe card below for full information on ingredients and quantities.
How to Make Cosmic Brownies
Step 1: Preheat oven to 350°. Grease 13x9x2 inch baking pan or line with foil or parchment. Assemble all ingredients.
Step 2: Add 4 squares chocolate and ⅔ cup butter to a large saucepan and cook over low heat until melted, stirring frequently. Remove from heat.
Step 3: Add sugar, eggs, and vanilla and whisk until well blended. Stir in flour, baking powder, salt, and nuts if using, and mix just until blended.
Step 4: Spread into prepared pan. Bake for about 30 minutes, or until brownies begin to pull away from the sides of the pan. (Do not overbake.)
Step 5: Make the chocolate frosting by melting the butter and chocolate. Stir in powdered sugar, milk, salt, and vanilla. Whisk until smooth. Place pan of frosting in bowl of ice and water; continue beating until smooth, creamy, and of spreading consistency.
Step 6: Stir in nuts if using. Frost the brownies and top with sprinkles if using. Slice brownies and serve!
Recipe FAQs
While you can use chocolate chips in a pinch, it’s not recommended. Baking chocolate squares (like Baker’s) are specifically formulated for melting and baking, containing different fat ratios than chocolate chips. Using chocolate chips may result in a grainier texture and could affect how well the frosting sets.
This usually happens when the frosting cools too quickly or is whisked for too long in the ice bath. The key is to watch the consistency carefully while whisking — you want to stop when it reaches a spreadable consistency but is still slightly warm. If your frosting does become too thick, simply warm the pan over very low heat, stirring constantly, until it reaches the right consistency.
Three common causes: overmixing the batter after adding the flour (mix just until combined), overbaking (remove from oven when a few moist crumbs still cling to a toothpick), or inaccurate flour measurement (use the spoon-and-level method rather than scooping directly with the measuring cup).
Expert Tips
- Cutting Brownies: Let the brownies cool completely before cutting. I recommend using a warm knife, wiping it clean between cuts, for the cleanest edges. This extra step makes all the difference in presentation. I have a great post on how to cut brownies into nice even squares.
- Freezing Tip: These brownies freeze beautifully for up to 3 months. The trick is to freeze them before adding the rainbow chips/sprinkles. Place them in an airtight container with wax paper between layers. Let them thaw completely at room temperature, then add the sprinkles just before serving.
- Fun Toppings: While the original cosmic brownies feature their iconic rainbow chips, you can get creative here. I’ve found that rainbow chips, colorful nonpareils, or even rainbow sprinkles all work beautifully. The key is adding them while the frosting is still slightly warm so they adhere properly but won’t melt.
More Brownie Recipes You’ll Love
- Shortcut Turtle Brownies start with a brownie mix, then you load them up with chopped caramel filled chocolate candies and crunchy pecans inside and on top.
- King Arthur Flour Fudge Brownies are a perfect balance of fudgy with just a touch of cakey.
- Marshmallow Surprise Brownies can be tailored for any holiday or special occasion.
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Homemade Cosmic Brownies
Equipment
Ingredients
Cosmic Brownies
- 4 squares 1 ounce each unsweetened chocolate, 4 ounces total
- ⅔ cup butter
- 2 cups sugar
- 4 eggs
- 2 teaspoons vanilla
- 1 ¼ cups all purpose flour
- 1 teaspoon baking powder
- 1 teaspoon salt
- 1 cup chopped nuts if desired
Glossy Chocolate Frosting
- 3 squares 1 ounce each unsweetened chocolate
- 3 tablespoons butter
- 2 cups powdered sugar
- ¼ teaspoon salt
- ⅓ cup milk
- 2 teaspoons vanilla
- ½ cup finely chopped nuts if desired
Instructions
- Preheat oven to 350°. Grease 13x9x2 inch baking pan or line with foil or parchment.
- Add 4 squares chocolate and ⅔ cup butter to a large saucepan and cook over low heat until melted, stirring frequently. Remove from heat.
- Add sugar, eggs, and vanilla and whisk until well blended. Stir in flour, baking powder, salt, and nuts if using, and mix just until blended. Spread into prepared pan.
- Bake for about 30 minutes, or until brownies begin to pull away from the sides of the pan. (Do not overbake.)
- Cool slightly; spread with Glossy Chocolate Frosting. Cool completely before serving.
Glossy Chocolate Frosting- Add 3 squares chocolate and 3 tablespoons butter to a large saucepan and cook over low heat until melted.
- Stir in powdered sugar, milk, salt, and vanilla. Whisk until smooth.
- Place pan of frosting in bowl of ice and water; continue beating until smooth, creamy, and of spreading consistency. Stir in nuts if using.
- Frost the brownies and top with sprinkles if using. Slice brownies and serve!
Notes
- Letting eggs come to room temperature will help them incorporate more smoothly into the chocolate mixture.
- Don’t overbake! The brownies should still be slightly fudgy when tested with a toothpick.
- Allow the brownies to cool completely before frosting for the best results.
- Store in an airtight container at room temperature for up to 5 days.
Michelle
Hello, quick question . Should it be 4 ounces of chocolate for the brownie or 4 squares. Our baker squares are smaller now and 4 pieces = 1ounce.. thanks so Michelle
Melissa Griffiths
Thanks for letting me know that they have changed that, it should be 4 ounces!
Carol
Oh my goodness…I may have this cookbook in a box I brought home from my Mom’s! She had a lot of Gold Medal cookbooks in her collection. Those brownies look delicious–and so festive with the colored chips sprinkled over top.
Don’t you just love the old cookbooks? I sure do! 🙂
Barbara Schieving
That would be so fun if you have it already. Definitely love old cookbooks.
K.Harkins
hello-salt is listed in frosting ingredients, but not in directions. Assuming it’s added with powdered sugar, milk, vanilla and nuts?
Barbara Schieving
Yes, I’ve updated the recipe – thanks!