How to Make It
Heat oven to 375° F. In a medium bowl, whisk together the flour, baking soda, cream of tartar, and salt.
With an electric mixer, beat the butter, brown sugar, and 1 cup of the granulated sugar on medium-high speed until light and fluffy, 2 to 3 minutes. Beat in the eggs and vanilla. Reduce speed to low and gradually add the flour mixture, mixing just until incorporated.
In a shallow bowl, combine the cinnamon and the remaining ¼ cup of granulated sugar. Form the dough into balls (each equal to 1 level tablespoon). Roll the balls in the cinnamon sugar mixture and place on parchment-lined baking sheets, spacing them 2 inches apart.
Bake until the edges are golden, 12 to 14 minutes. Cool slightly on the baking sheets, then transfer to wire racks to cool completely.