01 - Preheat oven to 375°F. Line two baking sheets with parchment paper.
02 - Whisk together flour, cream of tartar, baking soda, and salt in a medium bowl.
03 - Beat softened butter and granulated sugar until light and fluffy, approximately 2 minutes.
04 - Add eggs one at a time, mixing thoroughly after each addition, then stir in vanilla extract.
05 - Gradually add dry ingredients to wet mixture, mixing just until combined.
06 - Mix sugar and cinnamon in a small bowl for coating.
07 - Scoop 1 1/2-tablespoon portions of dough, roll into balls, and coat thoroughly in the cinnamon-sugar mixture.
08 - Place dough balls 2 inches apart on the prepared baking sheets.
09 - Bake for 9 to 11 minutes until edges are set but centers remain soft.
10 - Allow cookies to cool on baking sheet for 5 minutes before transferring to a wire rack to cool completely.