Preheat oven to 350.
In a medium bowl, combine the flour, cream of tartar, and baking soda. Set aside.
In a large mixing bowl, blend together the softened butter, shortening, sugar, eggs and vanilla until well combined.
Add the flour mixture to the butter mixture in thirds, mixing until just combined after each addition. Do not overmix!
In a small bowl, combine the 3 Tbsp sugar and 4 tsp cinnamon.
Roll 1-2 Tbsp of dough into balls. Roll in the small bowl of cinnamon/sugar and place onto parchment paper about 2 inches apart.
Bake 8 minutes and 30 seconds. Remove from oven, wait 30 seconds, and then remove from baking sheet and allow to cool on a baking rack.
