Line baking sheets with parchment paper or a baking mat and put in refrigerator to chill.
Whisk together the flour, cream of tartar, baking soda and salt in a medium bowl. Set aside.
Cream together the butter and sugar until pale and fluffy, about 3 minutes. Add the eggs, one at a time, beating well after each addition. Beat in the vanilla.
Gradually stir in the flour mixture, beating on low speed just until the flour is blended.
Chill the dough for at least 30 minutes.
In the meantime, mix together the sugar and cinnamon in a small bowl.
Preheat oven to 350 degrees F.
Scoop 1-inch balls of dough and roll in the cinnamon and sugar mixture to coat.
Place on chilled cookie sheet about 2 inches apart and bake for 10 minutes.
Chill the dough and cookie sheets between batches.
Let cookies set on baking sheet for 2-3 minutes and then remove to a cooling rack. Store cookies in an airtight container.
Chill, chill, chill! - Be sure to follow the chilling instructions for the pan and dough. It helps the cookies hold their shape and not spread.
Baking Pans Prep - I recommend using parchment paper to line the pans to eliminate any possibility of the cookies spreading.
Cream of Tartar - This is a key ingredient in snickerdoodles, but if you find yourself in a serious pinch, you can use 2 teaspoons baking powder and omit BOTH the cream of tartar AND the baking soda. Just remember the flavor will be slightly different.