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brownie with icing and sprinkles

Cosmic Brownies

5 Stars 4 Stars 3 Stars 2 Stars 1 Star 4.9 from 29 reviews
  • Author: Erin Clarkson
  • Prep Time: 20 minutes
  • Cook Time: 20 minutes
  • Total Time: 40 minutes
  • Yield: 16 servings 1x
  • Category: Brownies
  • Method: baking
  • Cuisine: american


Homemade Cosmic Brownies have a fudgy brownie layer topped with a smooth chocolate icing and rainbow sprinkles. They are quick and easy to make, and are the perfect easy brownie recipe!




  • 200g dark chocolate (I used 72%), coarsely chopped
  • 180g unsalted butter, cold from the fridge is fine
  • 15g dutch process cocoa powder, or regular unsweetened cocoa, sifted
  • 3 large eggs (about 150g not including shells), at room temperature
  • 200g caster sugar
  • 100g light or dark brown sugar
  • 2g (½ tsp) kosher salt 
  • ½ tsp vanilla extract or vanilla bean paste
  • 100g all-purpose flour, sifted

Chocolate Icing

  • 250g powdered sugar, sifted
  • 25g cocoa powder (regular or Dutch Process is fine)
  • pinch of salt
  • 60g unsalted butter, cut into small pieces, at room temperature
  • 40g boiling water

Rainbow Sprinkles of your choice to finish



  1. Preheat the oven to 350°f / 180°c. Line a 9”x13" (20cm x 30cm) pan with parchment paper, leaving a little extending up the sides of the pan to help remove the brownie.
  2. In a heatproof bowl over a pan of simmering water (make sure the bowl does not touch the water), combine the dark chocolate and butter. Heat, stirring frequently, until the chocolate and butter are melted and the mixture is smooth. Alternatively you can do this step in the microwave-safe bowl - microwave for 30 second increments, stirring well after each until the mixture is smooth and combined. 
  3. Sift the cocoa powder over top of the chocolate and butter mixture and stir until well combined.
  4. In a large bowl, combine the eggs, granulated sugar, and brown sugar. Mix on medium to high speed with an electric handheld mixer for 2-3 minutes until the mixture has lightened and increased in volume. This step can also be done in a stand mixer using the whisk attachment.
  5. Add the chocolate mixture and mix to combine. Add the salt and vanilla and mix until incorporated. 
  6. Add the flour and incorporate by hand until the mixture is smooth and does not have any lumps. 
  7. Transfer the batter to the prepared pan, and tap the pan on the counter a few times to ensure there are no air bubbles. Leave to sit for a minute or two then bang again to ensure there are no bubbles.
  8. Bake the brownies for 18 to 20 minutes, checking after 15. You are looking for the edges and top of the brownie to be set, and when a skewer is inserted into the middle, it should come out with a few moist crumbs attached. You are best to lean toward under baking than over baking. While the brownie is baking, prepare the icing ingredients so you are ready to start making it when the brownie comes out of the oven.
  9. Remove the brownie from the oven and leave to stand for 5 minutes before starting making the icing. 


  1. Sift together the powdered sugar, cocoa powder, and salt. Add the butter and mix until the butter is coated by the dry ingredients. 
  2. Once the brownie has sat for 5 minutes, add the boiling water to the icing ingredients, and mix until the butter is melted and the icing is evenly combined. I like to start with a spatula and switch to a whisk to help the icing come together. 
  3. Add the icing to the hot brownie, then carefully use an offset spatula or the back of a spoon to smooth the icing down. The heat from the brownie will melt the icing, helping it to smooth out.
  4. Once the icing is smooth, leave it to stand for 1-2 minutes, then add the sprinkles of your choice. 
  5. Place the cosmic brownies in the fridge until completely chilled, a few hours or up to overnight. 
  6. Remove from the pan using the parchment and slice into pieces using a sharp knife. 
  7. Store in an airtight container in the fridge for up to 5 days.