Preheat your oven to 350 degrees.
In the bowl of your stand mixer, beat the softened butter and sugar until light and fluffy. About 2-3 minutes.
Then, add in the egg and vanilla extract.
In a separate bowl, sift together the flour, cornstarch, baking soda, baking powder, and salt.
Slowly add the flour mixture into the wet mixture, using the low speed.
Mix until everything is incorporated and then add in the sprinkles.
Line a baking sheet with parchment paper and scoop 1.5 tablespoons of dough out into balls.
Place the cookie dough balls about 2 inches apart on prepared baking sheet. Bake for 10-12 minutes.
Cookies will still look undercooked when coming out of the oven, but trust me, they are done! Let them cool on the baking sheet for 5 minutes before moving them to a wire rack to cool completely to room temperature.
Store in an airtight container for up to 5 days or freeze for up to 3 months.
