Cosmic Brownie Cookies

chocolate cookie topped with chocolate buttercream and rainbow chips.

5 from 2 votes

Cosmic Brownie Cookies - soft, fudgy chocolate cookie base topped with a rich and decadent homemade chocolate buttercream with fun rainbow chips. It's nostalgia in a cookie!

Prep Time 15

Cook Time 15

Chill Time 30

Total Time 1

Servings cookies

Author Melissa Williams

Ingredients

For the cookies

½ cup unsalted butter softened to room temperature
¾ cup light brown sugar
¼ cup granulated white sugar
1 large egg
1 teaspoon vanilla extract
¼ cup unsweetened cocoa powder
2 cups all purpose flour
½ teaspoon salt
½ teaspoon baking powder

For the chocolate buttercream

2 ounces unsweetened baking chocolate
4 Tablespoons butter softened to room temperature
1 teaspoon vanilla extract
3 cups powdered sugar
3.5 Tablespoons milk I used 2%
1 pinch salt optional
Rainbow candy chips

Instructions

To make the chocolate cookies

In a large bowl cream together the butter and both sugars until fluffy.
½ cup unsalted butter, ¾ cup light brown sugar, ¼ cup granulated white sugar
Beat in the egg, vanilla extract, and cocoa powder.
1 large egg, 1 teaspoon vanilla extract, ¼ cup unsweetened cocoa powder
Add in the flour, salt, and baking powder. Mix until just combined. It will be very crumbly but should easily press together.
2 cups all purpose flour, ½ teaspoon salt, ½ teaspoon baking powder
Divide the dough into 6 equal portions and form each portion into a large ball.
Place the balls onto a baking sheet lined with parchment paper or a silicone baking mat. Loosely cover with plastic wrap and refrigerate for at least 30 minutes.
While chilling, I suggest making the buttercream and preheating the oven to 350°.
Once chilled, bake the cookies for 15-18 minutes. The edges should be just golden. If you over-bake, you'll lose the chewiness. Press down with the back of a spatula if you prefer flatter cookies.
Cool 5 minutes and then transfer to a rack to cool completely.

To make the chocolate buttercream

To a medium microwave safe bowl, add the chocolate and heat in 30 second increments, stirring in between, until melted and smooth. Cool 5 minutes.
2 ounces unsweetened baking chocolate
Once cooled, add the softened butter, vanilla extract, and powdered sugar. Use a hand mixer to beat until smooth.
4 Tablespoons butter, 1 teaspoon vanilla extract, 3 cups powdered sugar
Gradually add the milk while beating with the mixer until the desired consistency is reached.
3.5 Tablespoons milk
Taste and adjust to your preference. I add an additional pinch of salt because I don't like overly sweet buttercream.
1 pinch salt
Transfer the frosting to either a piping bag fitted with a large, round tip OR place it into a large zip top bag and snip the tip.

Assemble

Pipe the buttercream into a swirl on top of the cooled cookies. (alternatively, you can simply frost them with an offset spatula).
Sprinkle with rainbow chips and enjoy!
Rainbow candy chips

Notes

If you don’t have a piping bag, use a zip-top bag with the tip cut off or frost the cookies with a knife.
Rainbow chips are available on Amazon or at craft stores like Hobby Lobby.
Refrigerate the cookie dough before baking to keep them tall and chewy.
If the cookies don’t spread enough after baking, gently press them down with a spatula.
For extra chocolatey goodness, mix in rainbow chips or regular chocolate chips into the dough.
This recipe makes 6 large cookies—perfect for sharing! Double it for more, or divide the dough into smaller portions.
If you're looking for a break from chocolate, try using vanilla buttercream instead.

Nutrition