Preheat oven to 350*F. Line a baking sheet with parchment paper.
In the bowl of a stand mixer fitted with the paddle attachment or in a large bowl using a hand mixer, cream non-dairy butter and sugar until well combined and fluffy.
8 tablespoon Non-Dairy Butter, room temperature, 1 Cups Granulated Sugar
Add the non-dairy milk and vanilla and mix on low until well combined.
¼ Cup Non-Dairy Milk, 2 teaspoon Vanilla Extract
Add the flour, cornstarch, baking soda, and salt, and mix on low just until the dough forms. Then, add rainbow sprinkles and mix on low until distributed.
1 ¾ Cups All-Purpose Flour, 2 tablespoon Cornstarch, ½ teaspoon Baking Soda, ½ teaspoon Kosher Salt, ¼ Cup Vegan Rainbow Sprinkles
Add the remaining rainbow sprinkles to a small bowl.
¼ Cup Vegan Rainbow Sprinkles
Then, use a 3-tablespoon cookie scoop to scoop 8 cookie dough balls onto a parchment-lined baking sheet. Dunk the top of each cookie dough ball into the rainbow sprinkles and return them to the baking sheet leaving at least 2 ½ inches of space between each cookie.
Bake in a 350*F oven for 14-17 minutes, or until the edges begin to brown but the centers of the cookies is still soft.
Allow the cookies to cool on the baking sheet for at least 5 minutes before transferring to a cooling rack to cool completely. Repeat with the remaining cookie dough.