Heat oven to 350 degrees. Grease a 13 x 9 baking pan with nonstick cooking spray. In medium bowl, using wire whisk, stir together flour, baking powder and salt. Set aside. In a large bowl, with a wire whisk, mix together melted butter, sugar and vanilla. Beat eggs, one at a time, using a wooden spoon. Stir in flour mixture until well blended. Separate half the batter (about 1-1/2cups) to medium bowl. Mix in peanut butter. Stir in chocolate morsels and spread batter evenly in pan. Add cocoa powder to remaining batter and mix well. Stir in peanuts. spoon chocolate batter over peanut butter layer and smooth top gently. Bake 25 to 30 minutes, until a toothpick inserted in the center comes out clean . Cool in pan on wire rack. Cut into 24 squares.