Coat a 9x13 casserole dish with cooking spray

Combine butter and 4 cups Marshmallows in large saucepan on low heat. Stir until it's all melted and creamy. Remove from heat.

Add the cereal and mix well. Then add the remaining Marshmallows and chocolate chips. Mix well.

Press into prepared dish. Make sure it's flat and level.

Refrigerate until cold and set.