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Preheat oven to 350 degrees and line a cookie sheet with parchment paper 
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In a small bowl, mix together flour, baking soda, and salt; set aside. 
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Using a standing mixer, cream together butter, brown sugar and peanut butter. 
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Mix in the egg and vanilla until combined. 
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Gradually mix in the dry ingredients until just blended. 
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Form dough into 1 inch balls. 
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Shape into a log and roll log in sugar. 
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Place logs on cookie sheet about 2 inches apart. 
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Using the tines of a fork, make a criss-cross pattern in the dough. 
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Pinch the middle of the cookie to make a peanut shape. 
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Bake 10-12 minutes, until lightly browned on the edges and still soft in center. 
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Allow cookies to cool on baking sheet for 5 minutes before removing to a wire rack to cool completely.