Step 1

Preheat the oven to 400˚ F. Whisk the flour, 1/2 teaspoon cinnamon, the cream of tartar, baking soda and salt in a medium bowl until combined.

Step 2

Beat the butter, 1/2 cup granulated sugar and the brown sugar in a large bowl with a mixer on medium-high speed until light and fluffy, about 3 minutes. Beat in the egg and vanilla until well combined. Reduce the mixer speed to low. Add the flour mixture and beat until just combined.

Step 3

Combine the remaining 2 tablespoons granulated sugar and 1/2 teaspoon cinnamon in a small bowl. Pat the dough together into a ball. Roll in the cinnamon sugar until well coated, sprinkling the cinnamon sugar on the dough as you go. Put the dough in the center of an unlined baking sheet. Press into an 8-inch round, about 1/2 inch thick. Sprinkle any remaining cinnamon sugar over the dough.

Step 4

Bake until the cookie is cracked in the center and light golden brown around the edges, 10 to 12 minutes. Transfer the pan to a rack and let the cookie cool completely on the pan. Cut into wedges.