Place butter in 3-quart micro proof casserole.
Cook on HI, 1 minute.
Cover with casserole lid and cook on HI, 2 to 2 1/2 minutes, or until soft, stirring once.
Stir in peanut butter until blended.
Mix in cereal and peanuts.
Press warm mixture into lightly buttered 12 x 7 x 2-inch dish.
Cool before cutting into bars.