Step 1: Line a 9x13 inch baking pan with parchment paper, leaving an overhang on the sides. Set aside.
Step 2: In a large bowl, combine the melted butter, 1/2 cup of creamy peanut butter, 1 cup of powdered sugar, and graham cracker crumbs. Mix until well combined and a thick, crumbly mixture forms.
Step 3: Press the peanut butter mixture evenly and firmly into the bottom of the prepared pan. Use the back of a spoon or your hands to ensure a compact base.
Step 4: In a microwave-safe bowl, combine the butterscotch chips and the remaining 1/2 cup of creamy peanut butter. Microwave on high in 30-second intervals, stirring after each, until smooth and melted. If the mixture is too thick, stir in 1-2 tablespoons of milk to reach a pourable consistency.
Step 5: Pour the melted butterscotch topping evenly over the peanut butter base in the pan. Gently spread with a spatula to cover completely.
Step 6: Refrigerate the bars for at least 2 hours, or until completely firm. This is crucial for easy slicing.
Step 7: Once chilled, use the parchment paper overhang to lift the entire slab of bars out of the pan. Place on a cutting board and slice into squares or rectangles. Serve immediately or store in an airtight container in the refrigerator.