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These Copycat Cosmic Brownies are the BEST EVER! Super fudgy, chewy and gooey with a rich chocolate flavor and an addictive chocolate ganache frosting! Tastes like childhood but BETTER and they're so easy to make!
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5 from 1 vote

Best Ever Copycat Cosmic Brownies

These Copycat Cosmic Brownies are the BEST I've tried that taste even BETTER than the original ones we had as kids. Super fudgy and rich with a ganache frosting and addictive rainbow chocolate chips.
Prep Time20 mins
Cook Time30 mins
Total Time50 mins
Course: Bars
Servings: 12 -15
Author: Hayley Parker, The Domestic Rebel


  • 1/2 cup (1 stick) unsalted butter
  • 4 ounces semi-sweet chocolate such as a Baker's chocolate bar roughly chopped
  • 1 cup granulated white sugar
  • 2 large eggs
  • 1 large egg yolk
  • 2 teaspoons vanilla extract
  • 1 Tablespoon cornstarch
  • 1/4 cup cocoa powder I recommend Dutch process
  • 1/2 cup all-purpose flour
  • 1/4 teaspoon salt
  • 1 & 1/2 cups semi-sweet chocolate chips
  • 1/2 cup heavy whipping cream
  • 1/4 - 1/3 cup Wilton rainbow crunch chips or you can use rainbow sprinkles, miniature M&M's candies, or even chopped walnuts


  • Preheat oven to 350 degrees F. Line a 8x8 or 9x9 inch square baking pan with foil, extending the sides of the foil over the edges of the pan. Spray the foil liberally with cooking spray; set aside.
  • In a medium saucepan over medium-low heat, add in the butter and chopped chocolate bar and stir constantly until melted and smooth, about 5 minutes. Set aside off heat to cool for about 5 minutes, then whisk in the granulated sugar and mix well. Beat in the eggs, one at a time, followed by the egg yolk and vanilla. Lastly, add in the cornstarch, cocoa powder, flour, and salt and mix well. Spread the batter into the prepared pan in an even layer.
  • Bake for 25-30 minutes or until a toothpick inserted near the center comes out clean or with moist, not wet, crumbs. Cool completely in the pan.
  • Once cooled, make your ganache frosting. Add the heavy cream to a microwaveable medium bowl and microwave for about 60 seconds. Add the chocolate chips to the hot heavy cream and let set undisturbed in the microwave for about 3 minutes to allow chocolate chips to soften and melt. Whisk the ganache until smooth and glossy, then spread it evenly over the brownies in the pan. Sprinkle liberally with the rainbow chips.
  • Refrigerate the brownies for at least 1-2 hours before cutting or until the frosting has set. Brownies will keep for a week in the fridge or 3 days at room temperature.