Place peanuts in a food processor and finely chop. Combine flour, baking powder and salt in a medium-size bowl.
Combine butter and both sugars in a large bowl; beat on medium-high speed with an electric mixer until fluffy, about 2-3 minutes. Add eggs and vanilla and beat until smooth. Add peanut butter and beat until smooth. Stir in flour mixture just until incorporated. Stir in the chopped peanuts.
Divide the dough into 2 equal portions. Turn one portion onto a piece of waxed paper and shape it, rolling it inside the paper, into a log about 12x2-inches. Wrap dough in plastic wrap and refrigerate for at least 2 hours or up to 24 hours. Repeat with the remaining dough. (Dough logs may be wrapped tightly in plastic and frozen for up to 1 month. Slice and bake directly from the freezer).
Heat oven to 350.
Slice the dough so it doesn't become flattened as you cut. Place cookies on ungreased baking sheets at least 2-inches apart. Pinch together opposite sides of each slice at the middle to create a peanut shape, reshaping as necessary.
Bake at 350 until lightly colored, 13-15 minutes (a minute or 2 longer for frozen dough). Let them stand on the baking sheet for 5 minutes, then remove them with a metal spatula to a wire rack to cool completely. Keep at room temperature in an airtight container for 2-3 days.
Drizzle (opt): If desired, melt 1 cup peanut butter chips with 1/2 teaspoon vegetable shortening in microwave for 1 minute. Stir until smooth, then transfer to a resealable plastic bag. Snip off a small corner; drizzle over cookies. Let dry at room temperature for at least 30 minutes before stacking