Line a 9x9-inch baking dish with parchment paper for easy removal.
In a mixing bowl, combine peanut butter, melted butter, brown sugar, and a pinch of salt. Stir until smooth.
Gradually add powdered sugar, mixing until fully incorporated. The mixture should be thick but spreadable.
Press the peanut butter mixture evenly into the prepared baking dish, smoothing the top.
In a microwave-safe bowl, melt milk chocolate chips in 30-second intervals, stirring in between until smooth.
Pour the melted chocolate over the peanut butter layer and spread evenly.
Refrigerate for 1-2 hours, or until firm.
Once set, cut into squares and serve.