Preheat the oven to 350°F and line a baking sheet with parchment paper.
In a large bowl, beat together egg, sugar, baking soda, vanilla and peanut butter until well-combined.
Drop dough by heaping teaspoonfuls onto prepared baking sheet, pressing lightly with the back of a fork (dip the fork in water to help prevent sticking). Bake until lightly set, about 12 minutes. Transfer to a wire rack to finish cooling.
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