Preheat the oven to 325°F, line two baking sheets with parchment papers, and set aside.
Using a stand mixer set on whisk attachment, beat the butter and the sugar until light and fluffy. Add the vanilla extract.
1 cup Butter, ⅔ cup Sugar, 1 teaspoon Vanilla extract
Using a rubber spatula, fold in the flour and gently mix. DO NOT OVERMIX.
2¼ cups All-purpose flour
Make mall balls of the dough, and roll them in the sugar. Place them on the baking sheet.
¼ cup Sugar
Sprinkle some sprinkles on each ball, and then press each ball with a flat-bottom glass or measuring cup to flatten the cookie ball. The thickness should be ¼ of an inch.
¼ cup Rainbow sprinkle
Bake for 15 minutes. Leave on the sheet for 5 minutes. then transfer to the cooling rack.