Using a stand mixer fitted with a paddle attachment, or an electric hand mixer cream butter and sugar in a large bowl for 4-5 minutes, until light and fluffy. Scrape the sides of the bowl and add the eggs and vanilla. Cream for 1-2 minutes longer.
In a small mixing bowl combine the flour, cream of tartar, baking soda, and salt. With the mixer on low slowly add in the dry ingredients and mix until fully incorporated. Scraping down the sides as needed. Fold in sprinkles.
Cover and chill the dough for 25-30 minutes, or overnight if needed. If chilling overnight, allow the dough to come to room temperature before scooping. After dough as chilled, preheat oven to 350 degrees F.
Using a measuring spoon or a cookie scoop, scoop out even amounts of dough, about 1 1/2 tablespoons. Roll into small balls until round and smooth. Place cookie dough onto lined cookie sheets, spacing 2 inches apart.
Bake for 9-11 minutes until slightly golden brown, the cookies will still be very soft. Allow to cool 3-5 minutes on the cookie sheet before transferring to a cooling rack. Store in an airtight container for up to a week!