Prepare brownies according to package instructions. Cool completely.
Combine powdered sugar, peanut butter and 4 tablespoons butter together until smooth and creamy. Spread evenly over cooled brownies.
Place chocolate chips and 3 tablespoons butter in microwave-safe bowl and microwave until melted, about 30-45 seconds. Stir until smooth. Spread over peanut butter layer. Let ganache set before cutting and serving.