Place marshmallows and butter in a large pot over low heat. Cook together until butter and marshmallows have melted, stirring occasionally.
Remove mixture from heat and stir in cereal until just combined.
Carefully fold in broken cookies until evenly mixed together.
Pour and evenly press mixture into a lightly greased, 8”x8” baking dish.
Allow treats to set, about 1 hour. Cut and serve.