Begin by whisking together the dry ingredients (flour, cream of tartar, baking soda, cinnamon, and salt) in a medium size mixing bowl.
Beat the softened butter and sugar in a stand mixer or a hand mixer until light and fluffy.
Add egg, egg yolk, and vanilla. Beat again until combined, scraping down the sides of the bowl if necessary.
Add the dry ingredients, one cup at a time, mixing in between.
Use a cookie scoop (¼ cup for large, 2 Tablespoon for medium) to measure the dough for each cookie.
Use your hands to roll the cookie dough into a ball shape.
In a small bowl, make the coating by combining ½ cup sugar and 1 ½ teaspoons of cinnamon. Roll each cookie dough ball in the cinnamon sugar mixture and place on a parchment paper lined baking sheet about 2 inches apart.
Bake at 375 degrees for 10-12 minutes (for large cookies) or 8-10 minutes (for medium cookies). Allow the cookies to rest on the baking sheet for 10 minutes before transferring to a cooling rack. Cool completely before storing.