These fudgy cosmic brownie cookies are your favorite nostalgic treat but in cookie form! Each chocolate cookie is super fudgy and rich, topped with homemade chocolate ganache and rainbow chips. This is such a fun take on a childhood classic!

Cookies covered in chocolate ganache and rainbow chips on parchment paper.

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Who else remembers Little Debbie Cosmic Brownies? If you put rainbow chips on something, I 100% will want to eat it! These cosmic brownie cookies are a fun take on cosmic brownies, but homemade.

I'm using my favorite chocolate cookie base (the same one from my chocolate s'mores cookies and one bowl triple chocolate chunk cookies!) and topped them with a simple homemade chocolate ganache and rainbow chocolate chips.

The JOURNEY I went through trying to find these chips, let me tell you! I ended up having them shipped to my hotel room the last time I was in New York because I just could not find them here in London! Worth it.

Why I love this recipe!

Super Easy - you just need 2 bowls (one for the cookie dough, one for the chocolate ganache) to make these cosmic brownie cookies!
Chocolate Lovers - if you are a chocolate lover, then you have to try this recipe.
Rich & Fudgy - these chocolate cookies are super fudgy, no dry cookies here.

Grab Your Ingredients!

All the ingredients needed to make cosmic brownie cookies, weighed out into small bowls.

Cocoa Powder: I've only tested this recipe with Dutch processed cocoa powder and not natural unsweetened cocoa powder. I don't recommend swapping it out because they react differently to baking soda and baking powder. Not sure if the cocoa powder in your pantry is dutch processed? Check the ingredients! If it says 'alkali' or 'acidity regulators', then it's dutch processed cocoa powder.
Butter: I'm always a fan of using European butter! Why? It has a higher percentage of butterfat, making whatever you bake with it creamier and richer.
Chocolate: I recommend using semi-sweet or dark chocolate to make the chocolate ganache.
Rainbow Chips: these are the rainbow chips I used, but if you can't find them then swap them out for mini chocolate chips or rainbow sprinkles!
Heavy Cream: You'll need to use heavy cream (or double cream if you're in the UK) to make the ganache.

Let's Make This Recipe!

A mixing bowl with a beige mixture in it.

Step 1: In your stand mixer or large bowl with a hand mixer, mix the butter, granulated sugar and light brown sugar until light and fluffy. Add the vanilla extract, egg and egg yolk.

A mixing bowl with chocolate cookie dough in it.

Step 2: Mix in the flour, cocoa powder, salt, baking powder and baking soda. Mix until just combined. Chill the cookie dough in the fridge for 30-60 minutes, this will help them not spread as much when baking.

Chocolate cookie dough balls on parchment paper.

Step 3: Preheat your oven to 350ºFahrenheit and line two baking sheets with parchment paper. Scoop out 3 tablespoons of cookie dough and place on the prepared baking sheets.

Baked chocolate cookies on parchment paper.

Step 4: Bake in the oven for 8-10 minutes. Let the cookies cool for 5 minutes on the baking sheet before removing to a wire cooling rack to cool completely.

A large bowl with cream and chopped chocolate in it.

Step 5: Place the chopped chocolate in a bowl. Heat the cream in a medium saucepan on the stove until it beings to steam and simmer. Pour over the chocolate and let sit for a few minutes.

A large bowl with chocolate ganache in it.

Step 6: Use a rubber spatula to gently stir in one direction until completely smooth. If you still have chocolate chunks, place in the microwave in 10-second increments. Use a spoon to spoon over the cooled cookies, and a small offset spatula to spread it over the cookies. Top with rainbow chocolate chips and enjoy!

Ella's Tips & Tricks

Kitchen Scale: I always, always recommend using a kitchen scale when baking! Otherwise, it's so easy to add too much cocoa powder or flour, which are going to give you cookies that are as dry as the desert.
Let the Cookies Cool: make sure the cookies are completely cool before you add the ganache topping, or it might melt right off!
Swap out Rainbow Chips: if you can't find rainbow chips, top them with mini chocolate chips, baking chips in another flavor (how amazing would peanut butter chips be?), sprinkles, crushed candy canes, or flaky sea salt!
Heat the Heavy Cream: Make sure you don't let the heavy cream come to a boil. If it's too hot when it's poured over the chopped chocolate, it's going to give you a grainy chocolate ganache.

A stack of chocolate cookies, one cookie has been cut in half.

Try these chocolate cookies next!

Ella from Alpine Ella is holding a cake stand with cupcakes on it.

Made This Recipe?

Make sure to leave a ⭐️ rating and review below! You can tag me on Instagram @alpineella or follow along on Pinterest, Facebook and TikTok!

Thank you!

Ella