Preheat oven to 400 degrees Cook 9-11 minutes
Whisk flour, cream of tartar, baking soda, and salt. Set aside.
Cream butter, shortening, and 1 1/2 cups sugar. Add eggs.
Add dry ingredients, beat at low speed until just combined ~20 secs
Mix cinnamon and sugar in shallow bowl. Roll dough into 1 1/2 inch balls.
Place on greased cookie sheets 2 inches apart.
Bake until edges are set and centers soft and puffy.
Cool on cookie sheet 2-3 minutes then transfer to cooling rack
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