Preheat the oven to 375 degrees Fahrenheit (190 degrees Celsius). Line baking sheets with parchment paper or silicone mats.
In a mixing bowl, whisk together the all-purpose flour, cream of tartar, baking soda, salt, and 3/4 teaspoon of ground cinnamon. Set aside.
2 1/2 cups all-purpose flour, 1 1/2 teaspoons cream of tartar, 1/2 teaspoon baking soda, 1/2 teaspoon sea salt, 3/4 teaspoon ground cinnamon
In another large mixing bowl, cream together the unsalted butter, granulated sugar, and brown sugar until light and fluffy.
1 cup unsalted butter, 1 cup granulated sugar, 1/4 cup brown sugar
Beat in the egg, egg yolk, and vanilla extract until well combined.
1 large egg, 1 large egg yolk, 1 teaspoon vanilla extract
Gradually add the dry ingredients to the wet ingredients, mixing until a dough forms.
In a small bowl, mix the sugar and cinnamon
Cinnamon sugar for rolling
Shape the cookie dough into 1-inch balls, and roll them in the cinnamon sugar mixture until coated.
Place the coated dough balls onto the prepared baking sheets, leaving space between each cookie for spreading.
Bake in the preheated oven for 8-10 minutes or until the edges are golden but the centers are still slightly soft.
Remove from the oven and let the cookies cool on the baking sheets for a few minutes before transferring them to a wire rack to cool completely.