Beat butter in the bowl of a stand mixer until well-creamed.
Add sugar and beat on high speed until well-combined and light and fluffy (about 1 minute).
Add eggs, one at a time, beating well after each addition.
Stir in vanilla extract.
In a separate bowl, whisk together flour, cornstarch, baking powder, baking soda, and salt.
Set mixer to low speed and gradually stir dry ingredients into butter mixture. Add ingredients and stir until well-incorporated.
Fold in chocolate chips and then sprinkles. Cover with clear wrap and chill in refrigerator for 30 minutes.
Preheat oven to 350F (177C) and line a cookie sheet with parchment paper
Once dough has finished chilling, drop by heaping 1 ½ Tbsp scoops onto prepared cookie sheets. Bake on 350F (177C) for 11-13 minutes (cookies will appear slightly underbaked still -- this is fine and they'll finish baking on the cookie sheet). Allow cookies to cool completely on cookie sheet before removing.