Place cookies in food processor and pulse until they resemble fine crumbs.

Place marshmallows and butter in a large, microwave safe bowl; microwave for 1-2 minutes or until marshmallows are puffed.

Remove marshmallows from microwave and stir in cookie crumbs.

Break off pieces of the mixture and form into lumps that resemble coal.

Place on a baking sheet lined with wax paper. Allow to set until firm.