01 - Line an 8x8 inch baking pan with parchment paper, leaving excess on the sides for easy removal.
02 - In a large mixing bowl, whisk together the melted butter and 1 cup peanut butter until thoroughly blended.
03 - Fold in powdered sugar and graham cracker crumbs, then add vanilla extract. Mix until a uniform, thick dough forms.
04 - Press the peanut butter mixture firmly and evenly into the lined pan. Smooth the surface with a spatula.
05 - Melt semi-sweet chocolate chips and 1/4 cup peanut butter together in a microwave-safe bowl, heating in 30-second intervals and stirring after each, until smooth.
06 - Pour the melted chocolate-peanut butter topping over the base and spread evenly with a spatula.
07 - Refrigerate the pan for at least 2 hours, or until the bars are fully set.
08 - Once chilled, lift the slab out using the parchment paper. Slice evenly into 16 bars and serve.