In a mixing bowl, whisk together flour, baking powder, cream of tartar, baking soda, and salt until no lumps remain. Set aside.
In a separate mixing bowl, cream butter and sugar together until light and fluffy. Beat in egg and vanilla. Beat in flour mixture until just combined.
Take 1 tablespoon of the mixture and roll in sprinkles until the dough is covered. Place on a parchment-lined baking sheet. Repeat with remaining dough, leaving about 2 inches between each ball of dough. Chill dough for 1 hour before baking.
When ready to bake, preheat oven to 350F.
Bake 8 to 10 minutes until they are just beginning to brown around the edges. Let cool for about 5 minutes before transferring to a wire rack to cool completely.
Recipe Notes
High altitude: raise oven temp to 375F. Use ½ teaspoon baking powder, ½ teaspoon cream of tartar, and ¼ teaspoon baking soda.