01 - Set the oven to 350°F and line two baking sheets with parchment paper.
02 - Whisk together flour, cream of tartar, baking soda, and salt in a medium bowl; set aside.
03 - Beat softened butter and 1 1/2 cups granulated sugar until light and fluffy, about 2 to 3 minutes.
04 - Add eggs one at a time, beating thoroughly after each addition, then mix in vanilla extract.
05 - Gradually add dry ingredients to the wet mixture, stirring until just combined.
06 - Combine 1/4 cup granulated sugar with cinnamon in a small bowl.
07 - Scoop tablespoon-sized portions of dough, roll into balls, then thoroughly coat each 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 slightly soft.
10 - Let cookies cool on baking sheets for 5 minutes before transferring to a wire rack to cool completely.