Line two baking sheets with parchment paper. Preheat the oven to 350 degrees F.
In a medium bowl, whisk the flour, salt, cayenne, and baking soda. In a large bowl, stir the butter, granulated sugar, and brown sugar until creamy. Stir in the peanut butter, egg, and vanilla. Add the flour mixture to the peanut butter mixture and stir to combine. Stir in the peanuts.
Scoop the dough into 2-tablespoon balls and place on the prepared sheets at least 2 inches apart. Using a fork dipped in sugar, gently press a crisscross pattern in the top of each cookie, flattening it out to a 2-inch circle.
Bake until the cookies are light brown around the edges and on the bottom, 12 to 14 minutes, rotating the sheets halfway through. Let the cookies cool for 5 minutes on the sheets on racks, then move them to the racks to cool completely. Store in an airtight container at room temperature for up to 2 days or in the freezer for 1 month.
"The New Sugar and Spice" by Samantha Seneviratne © Ten Speed Press, an imprint of Penguin Random House LLC 2015. Provided courtesy of Samantha Seneviratne. All rights reserved