If you spray your bowl, pan, and spoon with cooking spray, or rub with butter, you'll have less mess!
Measure cereal into a large bowl. In saucepan heat chocolate chips, butter, and only 3 of the 4 cups of marshmallowsover low heat, stirring frequently until melted. Remove from heat.
Pour marshmallow mix over cereal. Quickly toss until completely coated. Then stir in remaining 1 cup (or more) of marshmallows.
Press mixture into 8 or 9 inch square pan. Put into fridge for about 10 minutes or until firm enough to cut into bars.