In large mixing bowl, melt butter (30 sec.)- Stir in marshmallows to coat with butter.
Cook uncovered, 30 seconds; stir well and cook 15 seconds (30 sec. for large marshmallows).
Stir until smooth.
Add cereal; mix well.
With wet or buttered fingers press into greased 13 x 9-inch pan.
Cool and cut into squares.