01 - Line a 9x9 inch baking pan with parchment paper, allowing the edges to overhang for easy removal.
02 - In a large mixing bowl, combine the melted butter, peanut butter, powdered sugar, graham cracker crumbs, and vanilla extract. Stir until all ingredients are thoroughly blended and the mixture holds together when pressed.
03 - Transfer the peanut butter mixture into the prepared pan and press it firmly into an even layer, smoothing the surface with a spatula.
04 - Place the chocolate chips and peanut butter in a microwave-safe bowl. Microwave in 30-second intervals, stirring between each interval, until the mixture is completely melted and silky smooth.
05 - Pour the chocolate-peanut butter topping over the base layer and spread it evenly 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.
07 - Remove from the refrigerator and cut into 16 even bars. Store any leftovers in an airtight container in the fridge.