Preheat the oven to 350˚F. Use a mixer to beat the butter and 3/4 cup of granulated sugar for 2-3 minutes until lighter in color and fluffier in texture.
Beat in the egg and vanilla for 1-2 minutes.
In a separate bowl, combine the flour, baking powder, cream of tartar, and salt. Stir into the batter until combined.
Add 1/4 cup of the sprinkles and stir until combined.
Scoop with a #60 (about one tablespoon) cookie dough scoop, coat them with the sprinkles, and roll them into a ball shape.
Place them on parchment-lined baking sheets. Use the flat bottom of a glass to slightly flatten each ball of dough.
Bake at 350˚F for 7-9 minutes. The bottoms of the cookies should be lightly browned, but the tops should not be.
Video
Notes
Store in an airtight container at room temperature for 3-4 days or in the freezer for 3-4 weeks.