MICROWAVE butter and marshmallows in large microwavable bowl on HIGH 2-3 minutes or until butter is melted. Stir until marshmallows are completely melted and mixture is well blended.

ADD cereal and stir until well coated.

PRESS cereal mixture evenly into a buttered 13x9-inch pan, using a buttered spatula. Cool completely, then cut into 24 squares.