01 - Line a 9x9 inch baking pan with parchment paper, leaving enough overhang on the sides to lift the bars out easily after setting.
02 - In a large mixing bowl, combine the melted butter, creamy peanut butter, powdered sugar, graham cracker crumbs, and vanilla extract. Stir until all ingredients are fully incorporated and the mixture holds together when pressed.
03 - Transfer the peanut butter mixture into the prepared pan and press it down firmly into an even layer, smoothing the surface with a spatula or the back of a spoon.
04 - Place the semi-sweet chocolate chips and peanut butter in a microwave-safe bowl. Microwave in 30-second intervals, stirring thoroughly after each burst, until the mixture is completely melted and glossy smooth.
05 - Pour the melted chocolate-peanut butter mixture over the pressed base and spread it into an even layer using a spatula, ensuring full coverage to the edges.
06 - Refrigerate the pan for at least 1 hour, or until the chocolate topping is firm to the touch and no longer soft when gently pressed.
07 - Lift the slab out of the pan using the parchment overhang and place it on a cutting board. Cut into 16 even squares. Store any leftovers in an airtight container in the refrigerator.