Make the Blondie:

1. Preheat oven to 350°F (175°C). Line a 9×13-inch pan with parchment paper, leaving overhang on two sides.
2. In a large bowl, stir together the melted butter and peanut butter until smooth. Stir in the brown sugar, then beat in the eggs one at a time. Stir in the vanilla.
3. Fold in the flour, baking powder, and salt until just combined. Spread evenly in the prepared pan.
4. Bake for 18–22 minutes until the edges are set and the center is just barely firm (do not overbake — the blondie should still look slightly underdone in the center). Let cool completely in the pan before adding the next layer.

Make the Peanut Butter Krispies:

1. In a medium microwave-safe bowl, heat the peanut butter and white chocolate in the microwave for 1 minute. Remove, stir, then microwave another 30 seconds. Stir until smooth. Add the cereal and chopped peanuts, stirring until combined. Spread evenly over the cooled blondies. Refrigerate while you make the rice krispies layer.

Make the Rice Krispies Treats:

1. In a medium saucepan, melt the butter over medium-low heat. Add 3 cups of the mini marshmallows, stirring until mostly melted and puffy. Stir in the cereal until combined. Turn off the heat and stir in the remaining 1/2 cup marshmallows. Dump over the peanut butter krispies layer and use a greased spatula to pack gently into an even layer. Refrigerate for 1 hour until all layers are set.
2. Run a knife around the sides of the pan to loosen. Using the parchment overhang, lift the bars onto a cutting board. Slice into squares, serve, and enjoy!