I’ve transformed my childhood favorite—those nostalgic cosmic brownies—into this cookie form: rich, fudgy chocolate cookies topped with silky ganache and colorful sprinkles. It’s everything I love about the original treat, made even better.

Why You’ll Love This Recipe

I love how these cookies hit all the right notes: intense chocolate flavor thanks to dark cocoa powder, a melt-in-your-mouth fudgy center, and the satisfying crunch from the rainbow "cosmic" sprinkles. They’re ideal for dunking in cold milk or bringing to a gathering—they always disappear fast!

Ingredients

(Here's a tip: Check out the full list of ingredients and measurements in the recipe card below.)

1 cup salted butter, melted
1 ¼ cups granulated sugar
¾ cup light brown sugar
2 teaspoon vanilla extract
2 eggs, room temperature
1 ⅓ cups all-purpose flour
2 teaspoon corn starch
1 cup cocoa powder (I prefer dark chocolate cocoa powder)
1 teaspoon baking soda
½ teaspoon kosher salt

For the ganache frosting:

8 oz semi-sweet chocolate (bars or chips)
¾ cup heavy cream
½ teaspoon vanilla extract
1 cup cosmic brownie sprinkles

Directions

In a stand mixer, I whisk together the melted butter, sugars, and vanilla for 1 minute. I add eggs and mix until just incorporated.
I add flour, corn starch, cocoa powder, baking soda, and salt. I mix on low until everything is combined.
I scoop about 2–2.5 tablespoons of dough onto parchment-lined baking sheets. I chill them for 30 minutes to prevent spreading.
I preheat the oven to 350 °F. I arrange dough balls 2 inches apart and bake for 9–10 minutes until edges are set. I cool them on the sheet for 3 minutes, then transfer to a wire rack.
While cooling, I make the ganache: I heat cream until simmering, pour it over chopped chocolate, let it sit for 5 minutes. I add vanilla and whisk until smooth. I let it cool 15–30 minutes until spreadable.
Once cookies are cool, I spread about 2–3 tablespoons ganache on each, leaving a small border. I top with sprinkles. I serve immediately or chill to set the ganache.

Servings and timing

This batch yields about 20 cookies.

Prep time: ~10 minutes (plus 30 minutes chill)
Bake time: 9–10 minutes per batch
Ganache set-up: 15–30 minutes cooling before spreading

If someone ever asks, I’d say the total hands-on time is roughly 45 minutes, but I plan ahead for chilling.

Variations

I swap dark cocoa for regular cocoa when I want a milder chocolate flavor.
I use chocolate chips instead of baking bars for convenience.
Mini M&M’s or traditional rainbow sprinkles work in place of cosmic sprinkle chips.
I add a tablespoon of corn syrup for extra chewiness, like some fudgy cookie versions.
I try flavored extracts like mint or orange instead of vanilla for a festive twist.

Storage/reheating

I store cooled cookies in an airtight container at room temperature for up to 3 days. If I want the ganache firmer, I refrigerate them up to 5 days (they may firm up slightly—I bring them to room temperature before eating).
To warm them up, I microwave a cookie for about 5 seconds for a gooey, just-out-of-oven feel.

FAQs

How can I prevent the cookies from spreading too much?

I scoop the dough, chill the balls for at least 30 minutes, and bake immediately—they hold their shape much better that way.

Can I skip chilling the dough?

Chilling really helps maintain that thick, fudgy texture. If skipped, the cookies tend to flatten and lose their brownie-like chew.

My ganache is too runny—what went wrong?

If it’s too warm, I let the ganache cool longer until it can be spread without dripping—usually 15–30 minutes does the trick.

Can I freeze these cookies?

Absolutely. I freeze the cooled, un-ganached cookies for up to 3 months. I thaw, then make and spread ganache before serving.

Can I make these gluten-free?

Yes! I substitute a 1:1 gluten-free flour blend in equal measure. I haven’t tested it, but I expect them to stay fudgy and delicious.

Conclusion

I adore these Cosmic Brownie Cookies—they deliver everything I want from a deluxe chocolate cookie: rich flavor, fudgy texture, festive flair, and a creamy ganache crown. Whether I'm baking for fun, dessert, or a party, I guarantee these will vanish fast. Happy baking!