Soften the butter and beat until smooth. Add sugar, baking soda, and cream of tartar and beat until combined. Beat in egg and vanilla until combined, and then add flour.

Cover and chill for 1 hour.

Shape dough into 1-inch balls. Combine the 2T sugar and cinnamon. Roll balls into this mixture to coat. Place balls 2 inches apart on ungreased cookie sheet.

Bake in a 375F oven for 10-11 minutes. Cool on wire rack.