Adjust an oven rack to the middle position and preheat the oven to 375 degrees F. Line 2 (11X17-inch) rimmed baking sheets with parchment paper, silpat liners or lightly coat with cooking spray.
In a medium bowl, whisk together the flour, cream of tartar, baking soda and salt.
In a large bowl (or the bowl of a stand mixer), beat together the butter, shortening, and 1 1/2 cups granulated sugar until the mixture is light and fluffy, about 2 minutes.
Add the eggs and mix until well incorporated. Reduce the speed of your mixer (stand mixer or handheld) and add the flour mixture, mixing until just combined.
In a small bowl or shallow plate, combine the cinnamon and granulated sugar to coat the cookies. Roll the dough into 1 1/2-inch balls and roll in the cinnamon an dsugar to coat. Place the balls of dough about 2 inches apart on the baking sheets.
Bake the cookies, one sheet at a time, until the edges are light golden brown and the centers are soft and puffy, about 9-11 minutes. The cookies will flatten after they come out of the oven.
Remove the cookies to a wire rack to cool completely.