Preheat oven to 350° F. Line two sheet pans with a silicone liner or parchment paper.
Add flour, cream of tartar, baking soda and salt to a medium bowl, and mix until blended.
In another bowl, cream together 2 cups of the sugar and the butter.
Mix in the vanilla and eggs.
Slowly add the dry ingredients and mix until just combined.
In a shallow bowl, mix together remaining ¼ cup sugar and cinnamon.
Roll dough into 1″ balls and roll each dough ball in the cinnamon-sugar to coat. Place them several inches apart on the prepared baking sheets.
Bake 8-10 minutes or just until cookies firm up. Don't over bake!
Notes
To keep the cookies fresh and soft, store them in an airtight container (You can add a piece of bread to the container with the cookies to keep them soft) up to 3 days.