Preheat the oven to 350 F. In a medium bowl, whisk together flour, oats, salt, baking soda, cream of tartar, and ground cinnamon. In a large bowl, combine butter and sugar until fluffy.
Add in egg and vanilla extract, and mix until smooth. Add in the flour mixture, mix until it is fully combined. Place the remaining sugar and cinnamon in a shallow dish.
Roll the cookie dough into balls, and roll each ball into the cinnamon sugar. Place them onto a large ungreased baking sheet, at least 2-inches apart. Bake for 10-12 minutes.
