Microwave the butter in a very large bowl for 30 seconds.
Add the entire bag of marshmallows and microwave for 1 minute.
Using a rubber spatula or a wooden spoon, mix the marshmallow and butter together until you cannot see any of the butter.
Stir in the cereal 1 cup at a time.
Spray a muffin tin with non-stick cooking spray.
Roll the cereal mixture into balls and press the balls into the tin so they are in the shape of a nest.
Refrigerate for 1 hour.