Preheat your oven to 350°F. Grease and line a 9x13 metal pan with parchment paper.
In a stand mixer bowl, combine melted butter, brown sugar, and granulated sugar. Mix until well combined. Add vanilla and eggs, mixing until incorporated.
With the mixer on low, add in flour, salt, cornstarch, and baking soda. Mix until just combined.
Fold in chocolate chips and sprinkles. Scoop batter into the prepared pan and use a spatula to ensure even spreading. Bake for 22-25 minutes or until the edges turn golden brown. Allow to cool completely before frosting.