Line a 9x9-inch baking pan with parchment paper or plastic wrap, leaving some overhang on the sides for easy removal.
In a medium mixing bowl, combine melted unsalted butter, graham cracker crumbs, powdered sugar, and ½ cup creamy peanut butter. Stir until fully combined and the mixture looks like wet sand. Press firmly and evenly into the bottom of the prepared pan to form the base layer.
In a microwave-safe bowl, combine white chocolate chips and 2 tablespoons peanut butter. Microwave in 20-second intervals, stirring after each, until smooth and fully melted. Alternatively, melt gently using a double boiler.
Pour the melted white chocolate and peanut butter mixture over the crust layer. Spread evenly with a spatula. For a swirl effect, lightly swirl with a toothpick or knife.
Chill the pan in the refrigerator for at least 2 hours, or until the topping is firm and set.
Use the parchment paper overhang to lift the bars from the pan. Cut into squares and serve chilled. Store leftovers in an airtight container in the fridge.