In a large mixing bowl, combine butter, sugar and egg. Beat with an electric mixer until light and fluffy.
Add vanilla extract and beat until combined.
In a separate bowl, sift flour, baking soda, cream of tartar and salt.
Add flour mix to wet ingredients. Beat until just combined. Stir in sprinkles.
Cover and chill in refrigerator for 1 hour.
Preheat oven to 350°F. Line a baking sheet with parchment paper. Scoop batter with 2 Tbsp scoop onto prepare baking sheet, placing them 2" apart. Bake for 12-14 minutes, or until edges are lightly browned (center should still be soft - careful not to over bake them!).
Allow to cool completely before serving. Enjoy!