Spray a 9x9 baking dish with cooking spray and set aside. Heat the peanut butter in 30 second intervals until melted and liquid.

In a large pot, melt the butter and mini marshmallows together over medium-low heat.

Once melted remove from the heat and stir in the Rice Krispies.

When the Rice Krispies are mostly coated, drizzle the melted peanut butter over them and add the marshmallow fluff in a few dollops.

Gently fold in the peanut butter and fluff until marbled throughout the Rice Krispies.

Pour the mixture into the prepared pans spread evenly. Avoid pressing them down, as that can make them dense.

Let cool for 1-2 hours before cutting.