Cosmic Brownies

Preheat the oven to 350°F (175°C). Grease an 8×8-inch nonstick baking pan and line it with parchment paper, leaving at least 2 inches hanging over the edges.
In a medium-sized bowl, beat the melted butter, granulated sugar, and brown sugar with a hand mixer on medium speed.
Add eggs one at a time, mixing well after each addition.
Stir in the oil and vanilla extract.
In a separate bowl, whisk together the flour, cocoa powder, baking soda (if using), and salt. Slowly add the dry ingredients to the wet mixture while mixing at a low speed until fully incorporated.
Pour the brownie batter into the prepared pan and spread evenly. Bake for 30 minutes or until a toothpick inserted into the center comes out just barely clean.
Allow the brownies to cool in the pan for about an hour or until they are close to room temperature.
Place the heavy cream in a microwave-safe bowl. Heat in 15-second increments until hot, stirring in between.
Add the chopped semisweet and milk chocolates to the hot cream and let sit for a minute. Whisk until smooth.
Stir in the salted butter until completely melted and incorporated.
Pour the ganache over the cooled brownies. Use a spatula to spread it evenly. Let sit for 5 minutes to set.
Sprinkle the rainbow chocolate chip sprinkles evenly over the ganache.
Cover the brownies and refrigerate for about 1 hour or until the frosting is set. Use the parchment paper to lift the brownies out of the pan and cut into squares.