Preheat oven to 350 degrees. Line cookie sheets with parchment paper or a silpat.

Cream butter and sugar in an electric mixer fitted with the paddle attachment. Beat in egg and vanilla. Add baking soda and flour and beat until the dough just comes together. Stir in sprinkles. Chill dough for at least 30 minutes.

Scoop uniform sized balls of dough onto your cookie sheets. These cookies spread, so space them at least 2 inches apart. Bake about 8-10 minutes, rotating pans halfway through baking. Remove from oven just before they begin to brown (or, if you like them crunchy, you can cook them an extra minute). Cool 5 minutes before removing from cookie sheet.