01 - Set oven temperature 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. Set aside.
03 - Using an electric mixer, beat softened butter with 1 1/2 cups sugar until light and fluffy, approximately 2 minutes.
04 - Add eggs one at a time to the creamed mixture, followed by the vanilla extract. Mix until evenly combined.
05 - Gradually incorporate dry ingredients into the wet mix, stirring just until combined to maintain tenderness.
06 - Combine 1/4 cup sugar with ground cinnamon in a small bowl, mixing thoroughly.
07 - Scoop tablespoon-sized portions of dough, roll each into a ball, then coat evenly in the cinnamon sugar mixture.
08 - Place coated dough balls on prepared baking sheets spaced 2 inches apart.
09 - Bake for 9 to 11 minutes until edges are set but centers remain soft and puffy. Avoid overbaking.
10 - Allow cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.