In the bowl of a stand mixer, beat the room temperature butter and granulated sugar on medium speed for about 2 minutes until the mixture is light and fluffy.

Pour in the vanilla extract and crack the egg into the mixture, mixing until just combined.

Gradually add in the corn starch, baking soda, baking powder, salt, and all-purpose flour while mixing on low speed until everything is well combined.

Gently fold in the rainbow sprinkles with the mixer on low until they are just mixed in.

Line a baking sheet with parchment paper. Using a medium-sized cookie dough scoop, scoop the dough onto the baking sheet.

Cover the pan with plastic wrap and chill the dough balls in the refrigerator for 30 minutes.

Preheat your oven to 350°F (175°C) towards the end of the chilling time.

Arrange 5-6 chilled dough balls on each baking sheet, spacing them about 2 inches apart.

Bake in the preheated oven for 10-12 minutes or until the edges are just set.

If you’d like perfect circular cookies, use a round cookie cutter larger than the cookie to gently scoot them into shape right after removing them from the oven.

Let the cookies cool on the baking sheet for about 5 minutes before transferring them to a cooling rack to cool completely.