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Preheat oven to 375 degrees.
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Beat butter, oil, white sugar, powdered sugar, eggs, and vanilla. Beat until fluffy.
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In a large bowl, mix flour, baking soda, salt, and cream of tartar.
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Stir flour mixture into liquid mixture a little at a time.
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Roll into 1-inch balls and dip into sugar to coat.
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Place dough balls on ungreased cookie sheet, about three inches apart.
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Press the bottom of a glass on each ball to flatten them.
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Sprinkle each flattened cookie with colored sugar for decoration, if you wish.
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Bake until lightly browned, 10-14 minutes.