Pre heat oven to 325 degrees F. Lightly grease a 9 by 13 inch pan with non stick cooking spray.
In a medium sauce pan on medium low heat, add the butter, chocolate and stir until completely melted. Once it is completely melted remove from heat, and set aside. Let cool for 10 min.
In a medium bowl, add the sugar, eggs, and vanilla extract. Whisk until well combined, once the chocolate has cooled, add it to the egg and sugar mixture. Stir until well combined, add the flour and salt, stir until just combined.Add the brownie batter to your prepared baking pan.
Bake for 20-25 min or until the sides start to pull away from the pan. Let cool for about an hour and thirty minutes.
In a medium bowl or stand mixer, place the butter, peanut butter,and vanilla extract, beat on medium speed until very creamy about 2-3 minutes. Gradually add the powdered sugar, and when it gets thick add the heavy cream a tablespoon at a time. Beat until light and fluffy. Spread the layer of peanut butter frosting over the cooled brownies.