Preheat oven to 350 degrees. Line baking sheet with parchment paper, set aside.
In a large bowl (or the bowl of your stand mixer fitted with the paddle attachment) cream butter and sugars together until light and fluffy. Beat in eggs and vanilla until completely combined. Add flour, baking soda, cream of tartar, cinnamon, corn starch and salt and mix until just combined without over-mixing.
Whisk cinnamon and sugar together in a small bowl.
Roll dough into 1 1/2-2" balls, roll in cinnamon sugar and place on prepared baking sheet. Bake for 10-11 minutes. Cookies will seem under-done with finished baking but when they set up they will keep a soft and chewy interior. If you like crispier cookies, bake for a minute or two longer. Allow cookies to cool on hot pan for 10 minutes before transferring to wire racks to finish cooling completely.
Snickerdoodles will stay soft and fresh for up to 4 days stored in an airtight container.