Step 1: Preheat your oven to 350°F (175°C). Line a 9×13 inch baking pan with parchment paper, leaving an overhang on the sides. Lightly grease the parchment paper.
Step 2: In a large bowl, melt the unsalted butter. Let it cool slightly.
Step 3: Add granulated sugar and brown sugar to the melted butter. Whisk vigorously for 1-2 minutes until glossy and well combined.
Step 4: Add eggs one at a time, whisking well after each. Stir in vanilla extract.
Step 5: In a separate bowl, whisk together all-purpose flour, Dutch-processed cocoa powder, baking powder, and salt.
Step 6: Gradually add dry ingredients to wet ingredients, mixing with a spatula until just combined. Do not overmix.
Step 7: Pour batter into the prepared pan and spread evenly. Bake for 25-30 minutes, or until a toothpick inserted comes out with moist crumbs.
Step 8: While brownies bake, prepare the ganache. In a small saucepan over low heat, combine semi-sweet chocolate chips and sweetened condensed milk. Stir until smooth.
Step 9: Once brownies are out, let them cool for 10-15 minutes. While still slightly warm, pour ganache over top and spread evenly.
Step 10: Immediately sprinkle rainbow candy-coated chocolate chips generously over the warm ganache.
Step 11: Allow brownies to cool completely at room temperature (2-3 hours) or in the refrigerator (1 hour) before lifting from the pan.
Step 12: Slice into squares and enjoy your homemade cosmic brownie recipe!