Preheat the oven to 350°F/180°C. Line 2 sheet trays with parchment paper or a silicone baking mat, and set aside.
In a large bowl, stir together the flour, cream of tartar, baking soda, and salt, then set aside.
In the body of a stand mixer, using the paddle attachment, cream the butter with the sugar for 3 minutes until light and fluffy. This can also be done in a large mixing bowl with a hand mixer.
Add the eggs, one at a time, mixing each in fully before adding the next. Then mix in the vanilla extract.
Add ⅓ of the flour mixure, and mix to fully incorporate it. Repeat twice, until all of the flour is added. Scrape down the sides as needed.
Make the coating by stirring together the cinnamon and sugar in a medium bowl.
Portion the cookie dough into 12 even-sized portions to make these large cookies. Roll the dough into smooth balls, then roll each ball into the cinnamon sugar mixture. Place them on the sheet trays, 6 inches apart, they will spread quite a bit, so you will have to bake in batches.
Gently press down on the cookie dough balls to flatten them out into large flat circles.
Bake each tray of snickerdoodles for 14-15 minutes until lightly golden brown. When done they will be slightly puffed, appear dry in the center of the cookies.
Let the snickerdoodles cool completely on the cookie trays before transferring them to a wire rack.
Notes
To give your snickerdoodles more cinnamon flavor, add a teaspoon of ground cinnamon to the cookie dough. Crumbl's recipe doesn't include cinnamon in the dough, relying on the outer coating to bring all the flavor.
To Store: Keep soft snickerdoodle cookies in an airtight container at room temperature for up to 5 days, or freeze for up to 3 months.