Whisk together the flour, cornstarch, baking soda, and salt. Set aside.

In a large bowl, using an electric mixer or stand mixer on medium speed, beat the butter, granulated sugar, and brown sugar together until creamy and light (about 3-4 minutes).

Beat in the egg and egg yolk until well incorporated. Add the vanilla extract and almond extract, mixing until combined.

Reduce the mixer speed to low. Gradually add the dry ingredients to the wet ingredients, mixing just until combined and a soft dough forms.

Fold in the chocolate chips along with the rainbow sprinkles. Be gentle to avoid breaking the sprinkles. If you like, reserve some of each for topping the cookies.

Cover and chill the dough 2 hours or overnight.

Using a 3-tablespoon cookie scoop, portion the dough and roll into balls. If you reserved any sprinkles, dip the tops of each cookie dough ball into the sprinkles. Place onto the prepared baking sheets, leaving about 2 inches between the cookies.

Bake one pan at a time for 14-16 minutes, or until the edges are just turning golden but the centers still look soft.

Place the pans on a wire rack. If you reserved any chocolate chips, carefully press them into the tops of the warm cookies. Let the cookies cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.