Note: This recipe requires chilling for at least 1 hour.
Using a stand or hand-held mixer with the paddle attachment, beat the butter for about a minute or two until it's light and fluffy. Then add in the granulated sugar and beat for another minute until fully combined. Follow with the egg and vanilla extract, beating for about 2 minutes more.
In a medium-sized bowl, combine the flour, baking soda, salt, and cream of tartar.
With the mixer on a low speed, slowly pour the dry mixture into the wet in about 2-3 parts.
Once it is one homogenous dough mixture, fold in the sprinkles until evenly distributed.
On a parchment-lined baking sheet, form dough balls about 1 tablespoon in size. Place in the fridge to chill for at least 1 hour, up to overnight.
When ready to bake, preheat your oven to 350℉, place the cookie dough balls on a baking sheet about 2-3 inches apart, and bake for 12-14 minutes until the edges are golden brown.