Preheat your oven to 400°F (200°C).
In a large bowl, beat together the sugar, butter, shortening, eggs, and vanilla until smooth and creamy.
In a separate bowl, whisk together the flour, cream of tartar, baking soda, and salt.
Gradually mix the dry ingredients into the wet ingredients until combined.
Shape the dough into walnut-sized balls.
Combine the sugar and cinnamon in a small bowl or zip-top plastic bag.
Roll or shake the dough balls in the cinnamon-sugar mixture until coated, then place them 2 inches apart on ungreased baking sheets.
Bake the cookies for 8 to 10 minutes, switching rack positions halfway through, until set but not too hard.
Remove from the oven and immediately transfer to wire racks to cool.
Dig in and enjoy!
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