In a large pot, melt butter over low heat. Grease a 9x13 baking dish and set aside. Add marshmallows and stir constantly until melted. Remove from heat. Add cereal to marshmallow mixture and stir well until completely incorporated. Transfer cereal mixture to baking dish and let cool until warm to the touch. Using your hands or silicone spatula, press cereal mixture evenly into baking dish. Let cool completely.  Cut cereal mixture into large squares or rectangles. Add one large square to a campfire roasting stick. Carefully roast over fire, checking and turning often until desired golden brown color.