Combine popcorn and chopped BUTTERFINGER® in large bowl.
Melt butter in medium saucepan over low heat. Stir in marshmallows. Heat, stirring constantly, until marshmallows are melted and mixture is smooth.
Pour over popcorn mixture; quickly toss to coat well. Spray hands with non-stick cooking spray. Form popcorn mixture into six 3" balls. Place on wax paper to cool. Store in airtight container.