1. Preheat oven to 350°F. Grease bottom only of 13×9-inch pan.
2. Prepare and bake brownies following package directions for cake-like recipe. Remove from oven. Sprinkle marshmallows on hot brownies. Return to oven. Bake for 3 minutes longer.
3. Place chocolate chips, peanut butter and butter in medium saucepan. Cook over low heat, stirring constantly, until chips are melted. Add rice cereal; mix well. Spread mixture over marshmallow layer. Refrigerate until chilled. Cut into bars.
For a special presentation, cut bars into diamond shapes.