Whisk the flour, cream of tartar, baking soda and salt in a bowl.
Beat the butter and sugar for 2 minutes until fluffy, then beat in the yogurt, milk and vanilla.
Mix in the dry ingredients until a soft dough forms, then chill the dough for 30 minutes.
Preheat the oven to 350 F and line 2 baking sheets with parchment. Stir the coating sugar and cinnamon together in a small bowl.
Roll the dough into 1 1/2 tablespoon balls and roll each one in the cinnamon sugar.
Bake for 10 to 11 minutes, until the edges are set and the centers look puffed and soft.
Cool on the sheet for 5 minutes so they crinkle and set, then transfer to a rack.
