Preheat the oven to 375*F. Take out 2 baking sheets with parchment for the dough.
In a bowl, combine room temperature butter with both types of sugar until creamy.
Add eggs and vanilla and stir to combine. No traces of eggs should be left in the batter.
Add the flour, baking soda, baking powder, salt, and cornstarch and stir until a soft dough forms.
Measure out a cup and a half of sprinkles and add to the dough. Add the white chocolate chips at this time as well if using.
Using a spatula fold in the sprinkles making sure not to overmix.
With a 2 ounce cookie scoop or a tablespoon, scoop out 16 portions of dough onto a baking sheet. If using a tablespoon scoop out 2 tablespoons of dough and roll between your palms to make a smooth round of dough.
Bake 6-8 cookies per baking tray for 10-12 minutes. The cookies will be pale but the edges will be golden brown, the tops of the cookies slightly domed, and not shiny.
Cool the cookies on the baking tray for 5 minutes before transferring to a wire rack to cool.
Enjoy!