Preheat the oven to 375 F. Line a couple of large baking pans with either parchment paper or silicone baking mats and set them aside. Place the 1/2 cup sugar and 1 tbsp. ground cinnamon into a small bowl and stir to combine well. Set this aside.

In a large bowl using wither a hand mixer or a stand mixer with the paddle attachment, beat the butter on med-high speed until smooth and creamy. Beat in the sugar until it s light and fluffy. Add the egg and egg yolk, then the vanilla beating until well combined. Scrape down the sides of the bowl as needed.

In a separate, large bowl, whisk together the flour, cream of tartar, cornstarch, baking soda, salt and cinnamon. Switch the mixer speed to low and gradually add the dry ingredients to the wet until combined, scraping down the sides and bottom of the bowl as needed. Roll the dough into balls, about 1 1/2 tbsp. of dough per ball. Roll each ball into the cinnamon sugar mixture. Place them onto the prepared pans a couple inches apart from each other.

Bake for 8-10 minutes, until they are slightly golden around the edges. They should still look undercooked in the centers. Allow them to cool for 5 or so minutes on the pan before transferring them to a wire rack to cool completely.