In a large nonstick sauté pan, combine the butter and peanut butter, and increase the heat on the stove to medium or medium-low.
When the butter is melted, add the marshmallows.
Cook the marshmallows, butter, and peanut butter mixture together until the marshmallows are completely melted and blended with the other ingredients.
*This can take about 6-8 minutes—be patient!
In a large mixing bowl, combine the Rice Krispies cereal with the melted marshmallow mixture, and gently mix the contents until all of the cereal is coated evenly.
Spread the contents out onto a parchment-lined sheet tray and press gently on the surface with a rubber spatula to form an even layer.
Allow the rice crispy treats to cool at room temperature.
Serve when these have cooled slightly or store them in a covered container.