INSTRUCTIONS

Preheat oven to 325°F. Line a baking sheet with a silicone mat or parchment paper, set aside.
In a bowl or stand mixer, beat butter and both sugars until light and fluffy, about 2-3 minutes. With mixer on medium speed add in egg, yolk and vanilla and beat for another minute, scraping the sides as needed. Turn mixer to medium low and mix in baking soda, cream of tartar, salt and 1 teaspoon of cinnamon. Mix for 30 seconds, scraping sides as needed. Turn mixer to low and add in flour, mixing until just combined.
In a separate small bowl, make your cinnamon sugar by mixing together cinnamon and sugar, stirring until evenly combined.
Using a cookie scoop or spoon, measure about 2 tablespoons of dough and roll into a ball. Then roll each cookie dough ball into the Cinnamon Sugar mixture. Place on prepared baking sheet about 2 inches apart. Bake for 10-12 minutes, turning cookie sheet halfway through baking.
I bake mine for exactly 10 minutes every time I make these cookies with perfect results, but I know ovens vary, so bake only until the edges are slightly golden. The tops may seem slightly undercooked, but they will firm up perfectly when they cool. If you prefer a crisper textured cookie, bake for 2 additional minutes.