Preheat your oven to 375°F and line two baking sheets with parchment paper.
In a medium bowl, whisk together the flour, cream of tartar, baking soda, and salt.
In a large bowl, beat the softened butter and 1 1/2 cups sugar until light and fluffy, about 3 minutes.
Add the eggs one at a time, beating well after each addition, then mix in the vanilla extract.
Gradually stir the flour mixture into the butter mixture until just combined.
In a small bowl, mix together the 1/4 cup sugar and cinnamon for the coating.
Roll the dough into 1-inch balls, then roll each ball generously in the cinnamon-sugar mixture.
Place the cookies on prepared baking sheets about 2 inches apart and bake for 8-10 minutes until the edges are set but centers still look slightly soft.
Cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.
