In a large bowl, whisk together flour, cream of tartar, baking soda, salt, and ground cinnamon. Set aside.
In a large bowl using an electric mixer, cream together butter and sugars on medium speed. Add eggs and vanilla extract; beat until smooth.
Add flour mixture to wet ingredients; mix just until combined.
Cover and refrigerate dough for 60 minutes. Dough can be refrigerated overnight.
Preheat oven 375F degrees.
In a small bowl, mix together 3 tablespoons granulated sugar and 1 teaspoon of cinnamon.
Scoop dough into 2.5 teaspoon balls, or use a #60 disher to scoop balls of dough. Roll balls of dough in cinnamon-sugar mixture and place on an ungreased baking sheet or silicone mat/parchment paper-lined baking sheet. Keep dough chilled in between batches.
Bake for 9-11 minutes. Cookies may appear soft, but they will set as they cool.
Cool cookies on baking sheet for 3 minutes; transfer to wire rack and cool completely. Eat & Enjoy!
Notes
Snickerdoodles should be stored in an airtight container and will keep 5+ days.