Pour granola in large bowl, set aside.
Put marshmallows in medium bowl.
Pour butter over marshmallows and stir.
Microwave in 30 second intervals until marshmallows are melted and mixture is well combined, stiring as needed in between intervals.
Pour over the granola and mix well to combine, you may need to use some muscle.
Pour mixture into buttered/oiled 9x13 pan.
Gently press into place as needed and let set until cool.
Cut into squares, store in airtight container.