Pop popcorn and remove any unpopped kernals.

Put your popcorn into a large bowl and set aside.

In a pot on the stove melt the butter over medium heat. Once the butter is melted add the marshmallows. Stir the marshmallows and the butter until the marshmallows are melted. Keep stirring while the marshmallows melt so the mixture doesn't burn.

Pour the melted butter and marshmallow mixture over your popcorn and stir. Make sure all the popcorn is coated.

Put some butter on your hands and form the coated popcorn into balls. Add M&M's if desired, to the outside of the balls.

Wrap each popcorn ball in plastic wrap then store in an airtight container.