Adjust the oven rack to the middle. Preheat the oven to 350℉ (177℃). Line two baking sheets with parchment paper.
In a medium sized bowl, whisk together the flour, cream of tartar, baking soda, and salt. Set aside.
In a stand mixer with the paddle attachment or a hand mixer, beat the butter on medium-high speed for 1 minute. Add the sugar and cream together on medium speed for 2 minutes.
Beat in the eggs, one at a time then add the vanilla. Scrape down the sides of the bowl with a spatula.
Add the flour mixture to the wet ingredients in three parts. The dough will be sticky and thick.
In a small bowl, whisk together the sugar and ground cinnamon.
Roll the dough into balls, about 1 tablespoon each. For large cookies, measure about 2 tablespoons. Roll the dough balls into the sugar and place on prepared baking sheets. Sprinkle on more cinnamon sugar on top if desired. I recommend 6 cookies per a sheet.
Bake for 8-9 minutes, one baking sheet at a time. The cookies will look slightly underdone in the center. Let them cool for 10 minutes on the baking sheet before transferring to a wire rack.
Cookies are good for 5 days when stored in an airtight container at room temperature.
Notes
Freezing: Follow the recipe until step #6. Place the dough balls on a baking pan lined with parchment paper. Freeze the dough balls for 30 minutes to avoiding sticking together. Then, freeze the balls in a sealed freezer bag or container. You can freeze cookie dough for 2 months. To bake, let the dough thaw in the fridge overnight or let them thaw for 30 minutes at room temperature. Then follow the recipe from step #7.
Tips: Only bake one sheet at a time in the center of the oven. This keeps them from browning. Don't over bake! Let the cookies finish baking outside of the oven by leaving them to cool on the baking sheet for 10 minutes before moving to a wire rack.