Heat your oven to 375°F and line two baking trays with parchment paper.
In a medium bowl, mix flour, cream of tartar, baking soda, and salt. Keep aside.
In a large bowl, beat butter, white sugar, and brown sugar until light and creamy.
Add eggs one at a time, then mix in vanilla until smooth.
Slowly add the dry ingredients and mix just until a soft dough forms.
In a small bowl, mix sugar and cinnamon for the coating.
Scoop small portions of dough, roll into balls, and coat well in cinnamon sugar.
Place dough balls on the baking tray, leaving space between each.
Bake for 8 to 10 minutes until cookies look set but soft in the center.
Let cookies cool on the tray for a few minutes, then move to a wire rack.