Preheat oven to 350ºF. Spray 9 x 13-inch Cake Pan with vegetable pan spray; set aside. Place butter and chocolate in 1-quart microwave-safe bowl. Microwave on 50% power 2-3 minutes, stirring every 30 seconds until chocolate is melted. Stir in sugar. Add eggs and vanilla extract; mix well. Stir in flour and salt; mix until just combined.
Add peanut butter morsels and peanuts to brownie mixture. Turn brownie mixture into pan, spreading evenly.
Bake 25-28 minutes. Remove from oven; cool in pan on Cooling Grid. Cut into squares.