In a big microwavable bowl microwave butter for 1 minutes in high temperature setting.
Add marshmallow on it and then microwave for 2 minutes giving interval every 30 seconds to stir it.
When marshmallow is totally melted add rice crispy cereal and coat it evenly with marshmallow.
Spread into a greased 13 by 9 inch pan. Sprinkle chocolate sprinkle on top. Cool completely and cut into bars.