Line an 8x8 or 9x9-inch square baking pan with parchment paper or foil, leaving an overhang for easy removal later.
In a large mixing bowl, combine 1 stick of softened butter and the peanut butter. Mix together until smooth and well combined.
Add the powdered sugar in batches, stirring after each addition, until everything forms a thick dough-like mixture.
Press the peanut butter mixture evenly into the prepared pan, smoothing the top with a spatula or the back of a spoon.
In a microwave-safe bowl, combine the remaining 3 tablespoons of butter with the chocolate chips. Microwave in 30-second intervals, stirring each time, until completely melted and smooth.
Pour the chocolate mixture over the peanut butter layer. Gently spread it out to cover the surface evenly.
For a little extra flair, sprinkle sea salt, chopped nuts, or mini chocolate chips on top.
Refrigerate the pan for at least 2 hours, or until the chocolate is set and the bars are firm.
Lift the bars out using the parchment overhang, slice into squares, and serve!
