1. Heat butter and peanut butter in a large microwaveable bowl on medium-high (70%) for 1-1/2 minutes or until butter is melted; stir until well blended. Add marshmallows; toss to coat.
2. Microwave an additional 1-1/2 minutes or until marshmallows are completely melted and mixture is well blended, stirring after 45 seconds. Add remaining ingredients; mix well.
3. Press cereal mixture firmly into a lightly greased 15 x 10 x 1-inch pan. Refrigerate for 1 hour or until firm.
Cut into 32 bars to serve.