If you were the kid who always begged for Cosmic Brownies in your lunchbox, this recipe is going to hit all the right notes. We have fudgy brownies, smooth ganache, and those cheerful little rainbow chips that give it that signature look.
Cosmic Brownies were special treats when I was growing up, and this recipe is my homemade version of that memory. I wanted to keep the chewy texture and chocolate-on-chocolate layers, but make them taste fresher and richer.
The rainbow topping is non-negotiable in my house – it’s what makes them feel like the real deal. When these hit the fridge to set, the hardest part is waiting to cut that first square.
Step-by-step photos and instructions are below, but you can jump right to the recipe card if you wish!
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Why you’ll love this recipe
They’re rich, chewy, and perfectly chocolatey, the kind of dessert that makes everyone light up when you pull the pan from the fridge. Whether you bake them for a party, lunchboxes, or a little chocolate pick-me-up, this recipe delivers every single time.
If you’ve ever had brownies turn out dry or too cakey, the extra egg yolk is your new best friend. It adds fat and moisture, which gives these brownies that ultra-rich, chewy center – the kind you remember from the original Little Debbie version, but better.
I have included step-by-step photos and instructions, as well as tips and tricks in the post. If you’d rather skip all that, scoot right on down to the full recipe card located at the bottom of the post.
Key Recipe Ingredients
The full list of ingredients and amounts is found in the printable recipe card below.
- Butter. Adds richness and chewiness. Use salted butter for the best flavor, or add an extra pinch of salt if using unsalted.
- Sugar. Regular granulated sugar sweetens the brownies and helps create the shiny top.
- Brown sugar. Adds moisture and a hint of caramel flavor. Either light or dark brown sugar works.
- Egg and egg yolk. The combination adds moisture and richness. Always use large eggs at room temperature for baking.
- Vanilla extract. Enhances the chocolate flavor and gives depth.
- Dutch processed cocoa powder. Gives a deep chocolate color and smooth flavor. Natural cocoa can be used but will taste lighter.
- Flour. Use all-purpose flour and measure correctly to avoid dry brownies.
- Salt. Balances the sweetness and brings out the chocolate flavor.
- Heavy cream. Makes the ganache thick and creamy. Half and half can work if needed but will be thinner.
- Semisweet chocolate chips. Melt into a smooth ganache for the frosting that’s perfectly balanced in sweetness. Milk or bittersweet chocolate chips can be used for different tastes.
- Rainbow candy-coated chips. Add that classic Cosmic Brownie look. Buy them on Amazon (affiliate link) or at craft stores. Mini M&Ms or colorful rainbow sprinkles work too.
How to make Homemade Cosmic Brownies
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This next part is only a photo tutorial of the recipe steps. The full list of ingredients, quantities and instructions can be found in the printable recipe card below.
Get prepped: Preheat the oven to 350°F and line a 9×13 inch baking pan with parchment paper.
Make the brownie batter: In a large bowl, whisk together the melted butter, sugar, and brown sugar until smooth. Add the egg, egg yolk, and vanilla extract, whisking until combined. Stir in the cocoa powder, flour, and salt until no streaks remain. The batter will be thick.
Bake the brownies: Spread the batter evenly in the prepared pan and bake for 18 to 22 minutes, or until the center is just set. Set aside to cool completely.
Make the ganache: Heat the heavy cream in a small saucepan or microwave-safe bowl until steaming but not boiling. Pour it over the chocolate chips and let it sit for 1 to 2 minutes, then whisk until smooth.
Add the topping: Spread the ganache evenly over the cooled brownies, then sprinkle with rainbow candy-coated chips. Chill until set, then slice into bars and serve.
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Troubleshooting Guide – Common Problems and Solutions
- Dry brownies. They were overbaked. Bake just until the center is set.
- Ganache too thick. Add a splash of warm cream and stir until smooth.
- Ganache too thin. Add a few more chocolate chips and stir until it thickens.
- Uneven slices. Chill before cutting and use a sharp knife. You’ll get clean slices if you are patient!
- Brownies sticking to the pan. Make sure to line the pan with parchment paper.
Frequently Asked Questions
How do I know when the brownies are done?
They should be just set in the center and no longer glossy. Overbaking will dry them out.
Do I need to chill them before slicing?
Yes, chilling helps the ganache set and gives clean, sharp edges.
Can I use natural cocoa powder instead of Dutch processed?
Yes, but it will have a lighter flavor and color.
Why do you use both an egg and an extra yolk?
The extra yolk adds richness and moisture, which helps create that signature fudgy, chewy center. Without it, the brownies can turn out more cakey than dense. It’s a small tweak that makes a big difference in texture.
Can I skip the extra egg yolk?
Technically, yes – but like, don’t. The yolk gives these brownies that classic Cosmic texture. If you leave it out, they’ll be more like traditional cake brownies instead of soft and chewy.
Kylee’s Notes
- Don’t overbake. The brownies are ready when the center is just set and no longer looks shiny. That’s how you keep them soft and fudgy instead of dry.
- Use melted butter. Starting with melted butter gives you that dense, chewy texture that makes these taste like the original Cosmic Brownies.
- Whisk thoroughly. Mixing the butter and sugars well helps create that classic shiny, crackly top everyone loves.
- Chill before slicing. Let the ganache set in the fridge before cutting. It makes cleaner slices and gives that perfect bakery look.
- Warm the cream carefully. Heat it until it’s steaming, not boiling, so the chocolate melts smoothly and doesn’t seize up.
- Customize your topping. Have some fun with it. Swap in crushed candy bars, mini chocolate chips, or colorful sprinkles for your own version of “cosmic.”
How to store Brownies
Store brownies in an airtight container at room temperature for up to 3 days, or in the refrigerator for up to 5 days. For longer storage, wrap individual brownies and freeze for up to 2 months. Thaw at room temperature before serving.
More recipes to love:
- Rocky Road Fudge – rich, chocolatey, and full of marshmallows and nuts, just like another throwback treat.
- Candy Cane Cookies – festive, fun, and easy to decorate like Cosmic Brownies.
- Haystack Cookies – no-bake, chocolatey, and crunchy.
- Raspberry Cheesecake Cookies – soft and sweet with a fruity twist.
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Cosmic Brownies
Ingredients
Brownies
- 10 tablespoons butter (melted)
- 1 cup white sugar
- ½ cup brown sugar (packed)
- 1 large egg
- 1 egg yolk
- 1 teaspoon vanilla extract
- ⅓ cup unsweetened Dutch processed cocoa powder
- 1 cup flour (all purpose – spooned and leveled)
- ½ teaspoon salt
Topping
- ¾ cup heavy cream
- ¾ cup semisweet chocolate chips
- ½ cup rainbow candy-coated chips
Directions
- Get prepped: Preheat the oven to 350°F and line a 9×13 inch baking pan with parchment paper.
- Make the brownie batter: In a large bowl, whisk together the melted 10 tablespoons butter, 1 cup white sugar, and½ cup brown sugar until smooth. Add 1 large egg, 1 egg yolk, and 1 teaspoon vanilla extract, whisking until combined. Stir in the ⅓ cup unsweetened Dutch processed cocoa powder, 1 cup flour, and ½ teaspoon salt until no streaks remain. The batter will be thick.
- Bake the brownies: Spread the batter evenly in the prepared pan and bake for 18 to 22 minutes, or until the center is just set. Set aside to cool completely.
- Make the ganache: Heat ¾ cup heavy cream in a small saucepan or microwave-safe bowl until steaming but not boiling. Pour it over ¾ cup semisweet chocolate chips and let it sit for 1 to 2 minutes, then whisk until smooth.
- Add the topping: Spread the ganache evenly over the cooled brownies, then sprinkle with ½ cup rainbow candy-coated chips. Chill until set, then slice into bars and serve.
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Notes
- Don’t overbake. The brownies are ready when the center is just set and no longer looks shiny. That’s how you keep them soft and fudgy instead of dry.
- Use melted butter. Starting with melted butter gives you that dense, chewy texture that makes these taste like the original Cosmic Brownies.
- Whisk thoroughly. Mixing the butter and sugars well helps create that classic shiny, crackly top everyone loves.
- Chill before slicing. Let the ganache set in the fridge before cutting. It makes cleaner slices and gives that perfect bakery look.
- Warm the cream carefully. Heat it until it’s steaming, not boiling, so the chocolate melts smoothly and doesn’t seize up.
- Customize your topping. Have some fun with it. Swap in crushed candy bars, mini chocolate chips, or colorful sprinkles for your own version of “cosmic.”
Nutrition Facts
Disclaimer
Nutritional information is an estimate and provided to you as a courtesy. You should calculate the nutritional information with the actual ingredients used in your recipe using your preferred nutrition calculator.
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