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Beat butter and shortening in a large bowl until creamy and smooth.
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Add in eggs one at a time beating after each addition.
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In a separate medium sized bowl combine the flour, cream of tartar, baking soda, sugar and salt.
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Beat 1/2 of the dry mixture into the wet mixture.
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Beat the remaining 1/2 of the dry mixture into the wet mixture. Dough should be workable and not too soft.
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Refrigerate dough uncovered for 30 minutes.
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Preheat oven to 375*.
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Combine sugar and cinnamon in a small bowl.
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Roll 1 inch balls of dough into the cinnamon mixture and place 2 inches apart on an ungreased cookie sheet.
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Bake for 10 minutes.
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Remove immediately from the cookie sheet onto a wire rack and let cool for 10 minutes before transporting them.