Line a 9 x 13-inch baking pan with heavy-duty aluminum foil, ensuring some overhang for easy removal. Lightly grease the foil with softened butter or a spritz of nonstick spray. Set aside 2 cups of marshmallows for later use.

In a large, light-bottomed pot or Dutch oven, melt the butter over medium heat, swirling the pan occasionally for even cooking. Watch closely as the butter transforms: it will foam, bubble, and shift from a bright yellow hue to golden brown. Once you notice a nutty aroma and golden-brown bits forming, immediately remove the pot from the heat. If the sediment turns too dark (almost black), strain the butter through a fine mesh sieve and return the clarified brown butter to the pan.

Stir the peanut butter into the warm brown butter until smooth and fully incorporated.

Take the pot off the heat and add the majority of the marshmallows (excluding the reserved portion), vanilla extract, and salt. Return the pot to medium heat, stirring gently with a wooden spoon or rubber spatula until the marshmallows have completely melted into a silky, cohesive mixture.

Remove the pot from the heat once more and fold in the Rice Krispies cereal, mixing thoroughly until every grain is coated with the marshmallow-peanut butter mixture.

Toss in the reserved marshmallows and give the mixture a few additional stirs. Be gentle and deliberate here—you want the reserved marshmallows to soften slightly without fully melting, creating delightful pockets of gooey sweetness.

Transfer the cereal mixture into the prepared baking pan, spreading it evenly. Use the saved butter wrappers or lightly dampened fingers to gently press the mixture into a smooth, even layer. Avoid compressing it too firmly, as this can make the treats dense instead of light and chewy.

Allow the treats to cool at room temperature for at least 1 hour. Once firm, use the foil overhang to lift the block of treats from the pan and place it on a cutting board. Slice into squares using a serrated bread knife for clean, uniform edges.

Store the peanut butter rice crispy treats in an airtight container at room temperature for up to 5 days, though they’ll likely disappear much sooner!