Prep. Preheat the oven to 350°F and line an 8X8-inch baking pan with parchment paper. Make sure to leave a bit of parchment paper hanging over the sides of the pan.
Make the brownie batter. Whisk together the butter, vegetable oil, sugars, cocoa powder, vanilla, egg, egg yolks, and corn syrup until smooth. Whisk in the flour, cornstarch, and salt until smooth.
Bake. Pour the batter into the prepared pan and bake for 20-25 minutes or until a toothpick inserted in the center comes out mostly clean.
Cool. Remove the brownies from the oven and allow them to cool completely in the pan.
Make the ganache. While the brownies are cooling, heat the heavy cream until it’s almost boiling and pour it over the chocolate chips. Let the mixture sit for a couple of minutes before whisking it until smooth. Whisk in the corn syrup.
Frost the brownies. Use the parchment paper to lift the fully cooled brownies from the pan. Spread the ganache over the brownies and top with rainbow sprinkles.
Notes
One of the best things about making this homemade cosmic brownie recipe is that you can make the fudgy cosmic brownies anything you want them to be and better than any packaged brownies you get from the grocery store. Here are a few ideas:
Add chocolate chips to the brownie batter
Use chocolate frosting instead of the chocolate ganache
Top the brownies with mini m&m instead of colorful sprinkles