01 - Preheat the oven to 375°F. Line two baking sheets with parchment paper and set aside.
02 - In a medium bowl, whisk together the all-purpose flour, cream of tartar, baking soda, and salt until evenly distributed. Set aside.
03 - In a large bowl, beat the softened butter and granulated sugar together using an electric mixer on medium speed until the mixture is pale, light, and fluffy, about 2 to 3 minutes.
04 - Add the eggs one at a time, beating well after each addition. Mix in the vanilla extract until fully incorporated.
05 - Gradually add the dry ingredient mixture to the wet ingredients, blending on low speed just until the dough comes together. Do not overmix.
06 - In a small shallow bowl, stir together the granulated sugar and ground cinnamon until evenly blended.
07 - Scoop the dough by rounded tablespoonfuls and roll into smooth balls. Roll each ball in the cinnamon-sugar mixture, coating thoroughly on all sides.
08 - Place the coated dough balls on the prepared baking sheets, spacing them about 2 inches apart to allow for spreading.
09 - Bake for 9 to 11 minutes, or until the edges are set and lightly golden while the centers still appear slightly soft and underbaked.
10 - Let the cookies rest on the baking sheets for 2 minutes, then transfer to a wire cooling rack to cool completely before serving.