Heat oven to 350 degrees F. Line 13 x 9 x 2-inch-square baking pan with foil. Generously coat with nonstick cooking spray.
In medium-size bowl, beat together peanut butter and butter. Beat in sugar until well blended. Beat in eggs and vanilla. Stir in flour, baking powder and salt. Add peanuts (mixture will be stiff). Press batter evenly into prepared pan.
Bake in 350 degree F oven for 30 minutes or until bar pulls away from sides of pan. Let cool completely in pan on wire rack.
Meanwhile, in medium-size bowl, beat together peanut butter, butter and confectioners sugar until smooth and fluffy. Spread over on top of cooled bar. Sprinkle with chopped peanuts, if desired. Cut into 36 rectangles.