Add butter to a saucepan over low to medium heat and brown, stirring constantly. Remove from heat once golden and nutty. Let cool slightly.
In a large bowl, mix brown butter with brown sugar and granulated sugar for 2 minutes.
Add egg, egg yolks, and vanilla extract and mix until combined.
Fold in flour, cornstarch (if using), baking powder, and salt until just combined.
Fold in Oreos, M&Ms, chocolate chips, and sprinkles if using.
Refrigerate dough for 30 minutes.
Scoop into 24 balls and place on a lined baking sheet.
Bake at 350°F for 9 to 11 minutes until edges are set and centers are soft.
Cool and enjoy.