01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - In a medium bowl, whisk together flour, cream of tartar, baking soda, and salt. Set aside.
03 - In a large bowl, beat softened butter and 1 1/2 cups sugar until light and fluffy, about 2-3 minutes.
04 - Add eggs one at a time, beating well after each addition. Mix in vanilla extract thoroughly.
05 - Gradually add the dry ingredient mixture to the wet mixture, blending until just combined.
06 - In a small bowl, stir together 1/4 cup granulated sugar with ground cinnamon.
07 - Scoop one tablespoon portions of dough, roll into balls, then completely coat each in the cinnamon-sugar mixture.
08 - Place dough balls 2 inches apart on prepared baking sheets to allow for spreading.
09 - Bake for 9 to 11 minutes until edges are set but centers remain slightly underbaked for chewiness.
10 - Let cookies cool on baking sheets for 5 minutes then transfer to a wire rack to cool completely.