For The Cinnamon Sugar:

1. In a small bowl, mix the ingredients until well combined. Set aside.

‍For The Snickerdoodles:

1. Preheat the oven to 350℉ / 177℃ and line a sheet pan with parchment paper.
2. In a medium bowl, add butter and sugar and cream on high speed with a hand blender or in a stand mixer until the mixture is light and fluffy.
3. Beat in the eggs and egg yolk until combined and then add in the vanilla extract.
4. In a separate bowl, whisk together the flour, sea salt, cream tartar, and baking soda.
5. Add the dry ingredients to the wet and fold together until evenly combined. Cover with plastic wrap and chill for 20 minutes, or up to overnight. 
6. Form the dough into 1-ounce balls and roll in the cinnamon sugar to coat completely. Place the dough on the prepared sheet pan so that they are about 2 ½-inches apart in 3 rows. 
7. Lightly grease the bottom of a glass with cooking spray and lightly press down on the balls to flatten slightly.
8. Bake for 9-10 minutes or until just barely golden and set on the tray. Let cool slightly on the sheet pan and then transfer to a wire rack to cool completely. Store leftovers in an airtight container on the counter for up to 1 week.