Spray an 8X8 baking dish with non-stick cooking spray.
Place the butter and marshmallows in a microwave safe bowl. Heat the mixture in the microwave in 30 second intervals, stirring after each interval, until the mixture is melted and combined.
Then stir in the cereal until the cereal and combined and coated with the marshmallow mixture.
Pour the mixture into the baking dish and spread the mixture down evenly into the dish. Note: I spray wax paper with non-stick cooking spray and use the wax paper to press the mixture into the pan so that it doesn't stick to my hands.
Allow to cool completely before serving.
Notes
*Store the leftovers in an airtight container at room temperature for up to 1 week.