Heat oven to 375 F. Whisk together the flour, baking soda, cream of tartar, and salt.
Beat the butter, brown and white sugar with an electric mixer on medium speed until light and fluffy, 2-3 min. Beat in the eggs and vanilla. Reduce speed to low and gradually add the flour mixture, mixing just until incorporated.
Form the dough into balls about 1 tablespoon each. Roll the balls in the cinnamon and place on parchment-lined baking sheets, spacing them 2 inches apart.
Bake until golden, 12 to 15 min. Cool on wire rack.