01 - Preheat oven to 350°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 - Beat softened butter with 1 1/2 cups sugar until light and fluffy, about 2-3 minutes.
04 - Add eggs one at a time, beating thoroughly after each addition. Blend in vanilla extract.
05 - Gradually fold dry ingredients into wet mixture until just combined.
06 - Mix 1/4 cup sugar with cinnamon in a small bowl for coating.
07 - Scoop tablespoon-sized dough portions, roll into balls, then fully coat in cinnamon-sugar mixture.
08 - Place dough balls 2 inches apart on lined baking sheets.
09 - Bake for 9-11 minutes, edges should be set while centers remain slightly soft.
10 - Let cookies cool on baking sheets for 5 minutes before transferring to a wire rack to cool completely.