Bake the Brownies:
Preheat oven to 350°F (175°C).
Prepare brownie mix according to package directions.
Pour into a greased 9×13-inch baking pan and bake as directed. Let cool completely.
Make the Peanut Butter Layer:
In a large bowl, beat peanut butter and softened butter until creamy.
Mix in powdered sugar and vanilla until smooth.
Spread evenly over cooled brownies.
Make the Ganache:
In a small saucepan, heat heavy cream and butter until just simmering (do not boil).
Remove from heat, pour over chocolate chips, and let sit for 2 minutes.
Stir until smooth and glossy.
Assemble:
Pour ganache over peanut butter layer and spread evenly.
Refrigerate for at least 1 hour to set.
Serve:
Slice into squares and enjoy!