Prepare the pan. Line a 9x13-inch baking pan with parchment, leaving overhang for easy lifting. Lightly grease the sides.
Make the peanut butter base. In a large bowl, stir together melted butter, 1 cup peanut butter, powdered sugar, graham cracker crumbs, vanilla, and salt. Mix until fully combined and no dry bits remain.
Press into the pan. Pour the mixture into the prepared pan.
Press firmly into an even layer using a spatula or the bottom of a measuring cup.
Make the chocolate topping. In a microwave-safe bowl, heat chocolate chips and 2 tablespoons peanut butter in 20–30 second bursts, stirring between each, until smooth. You can also melt over a double boiler.
Spread the chocolate. Pour melted chocolate over the base and smooth it out to the edges. Tap the pan gently to pop air bubbles.
Chill. Refrigerate for 2–3 hours, or until the chocolate is set and the bars are firm.
Slice cleanly. Lift the slab out using the parchment.
Warm a sharp knife under hot water, dry it, then slice into bars. Wipe and re-warm the knife as needed.