Prepare the Brownies: Follow your favorite brownie recipe, making sure to fully line the pan with parchment paper on all sides for easy removal. Allow the brownies to cool completely before proceeding to the next step.
Make the Peanut Butter Layer: In a mixing bowl, combine the softened butter and peanut butter. Beat until well combined, about 1 minute. Add the powdered sugar, salt, and vanilla extract, and mix until smooth and no clumps of powdered sugar remain. Spread the peanut butter mixture evenly over the cooled brownies, using a spatula to form a smooth layer. Set aside.
Prepare the Chocolate Ganache: In a microwave-safe bowl, combine the chocolate chips and heavy cream. Microwave in 30-second intervals, stirring well between each interval, until the chocolate is completely melted and smooth. Pour the chocolate ganache over the peanut butter layer and spread it into an even layer.
Chill and Serve: Place the brownies in the refrigerator and chill until the ganache is set, at least 1 hour. Once set, slice the brownies into squares and serve. Store in an airtight container for up to 1 week.