Preheat the oven to 350 degrees and line a sheet pan with parchment
Combine the flour, cream of tartar, and baking soda in a small bowl.
Cream the butter and sugar in a bowl using a hand mixer. Add the egg, egg yolk, and vanilla, mixing until combined.
Gradually add the flour mixture on a slow speed.
Scoop or spoon the batter on to the lined baking tray leaving about 2 inches between each one. They will spread quite a bit.
Stir the sugar and cinnamon together in a small cup. Sprinkle each mound of cookie dough with the cinnamon sugar.
Bake for 10-13 minutes until barely light brown on the bottom edge. The tops may still be shiny or look a little under cooked, but as they cool on the hot baking tray they will continue cooking.