Pour cereal into a very large bowl. In a large microwave-safe bowl, combine chocolate chips, peanut butter and butter. Microwave on high 30 seconds. Stir gently. Continue microwaving on high, stirring every 30 seconds, until melted and blended. Pour over cereal; gently stir to coat
In batches, place confectioners' sugar in a gallon-sized bag, add cereal mixture and shake until well coated. Spread cereal out on a baking sheet. Let stand until set. Store in airtight containers.