To begin, preheat your oven to 350 and line a 9x9 pan with parchment paper with two sides sticking out (for easy removal).
To a large mixing bowl, add your butter, white sugar and brown sugar and beat together with a mixer till creamy. Add your vanilla and egg and briefly blend them in.
To the same bowl, add your flour, cinnamon, cream of tartar, baking soda and salt. Stir everything together till you have a thick, consistent cookie dough batter.
Add dollops of the cookie dough batter evenly across the bottom of your 9x9 pan. Spread out carefully with a spatula, till you have a thin, even layer.
Bake for 20-25 minutes, or till a toothpick inserted comes out clean.
Let cool entirely prior to cutting and serving. Then, devour!