Prep Your Pan: Start by greasing a 9×13 inch baking dish with a little butter or non-stick spray. This will prevent the treats from sticking and make for easy removal and slicing.

Melt the Butter and Marshmallows: In a large pot, melt the 3 tablespoons of butter over low heat. Once melted, add the entire bag of marshmallows.

Stir Until Smooth: Stir the marshmallows constantly as they melt. Keep the heat low to prevent the sugar from burning. Continue stirring until the mixture is completely smooth and no lumps remain.

Remove From Heat: As soon as the marshmallow mixture is smooth, immediately remove the pot from the heat. This is a crucial step to ensure your treats stay soft and chewy.

Add the Cereal: Quickly add the 6 cups of Rice Krispies cereal to the pot with the melted marshmallow. Using a greased spatula (this prevents sticking!), gently fold the cereal into the marshmallow mixture until every piece is evenly coated.

Press Into Pan: Transfer the mixture to your prepared baking dish. Use the greased spatula, or your hands lightly greased with butter, to press the mixture firmly and evenly into the pan. Pressing firmly is key to getting treats that hold their shape when cut.

Cool and Set: Allow the treats to cool at room temperature for at least 1 hour until they are firm to the touch.

Slice and Serve: Once completely set, turn the slab out onto a cutting board and slice into squares with a sharp knife.