Preheat oven to 350° F. Combine the flour, sugar, baking powder, and salt in a large mixing bowl. Add the peanut butter and combine with a pastry cutter or 2 forks until it has reached a coarse, crumbly texture. Stir in the milk, egg, and butter. Coat a nonstick muffin pan with cooking spray. Fill each muffin cup about ¾ full with batter. Evenly sprinkle some chopped peanuts over each. Bake 15 to 20 minutes or until light golden brown. Cool on a wire rack.