Line cookie sheet with cooking parchment paper.
Break white chocolate into small pieces into medium microwavable bowl. Microwave uncovered on High about 1 minute or until almost melted. Stir until smooth. Spread on paper-lined cookie sheet to 1/4-inch thickness, about a 10x6-inch rectangle.
Immediately top with cereal, press into melted chocolate. Let stand about 1 hour, or refrigerate until firm. Break into pieces.