Spray a 9 x13-inch pan with non-stick cooking spray.
In an extra large microwave-safe bowl heat butter and marshmallows on HIGH for 3 minutes, stirring after 2 minutes. Stir until smooth.
Add cereal. Mix until well coated.
With a damp hand, evenly press mixture into prepared pan. Cool. Cut into 12 squares.
Put candy melts in two Ziploc bags, microwave candy melts at 40% power for 1 minute. Knead candy in the bag. Continue to microwave and knead at 30-second intervals until smooth and completely melted.
Snip off a small corner of the Ziploc bag and drizzle the melted candy on top of the rice krispie squares.