In a large mixing bowl, cream together the sugar, margarine and shortening until light and fluffy, about 5 minutes. Add in the eggs and mix for another 2 minutes.
Sift in the flour, cream of tartar, baking soda and salt and mix until combined.
In a separate bowl, mix the cinnamon and sugar for the topping.
Shape dough into small round balls and roll into cinnamon-sugar mixture.
Line a baking sheet with parchment paper and place dough balls 2 inches apart. Bake for 8-10 minutes.
Recipe by Eleni Saltas at https://elenisaltas.com/2019/04/10/moms-snickerdoodle-cookies/