In a large sauce pan, melt the butter, peanut butter chips and marshmallows on medium-low heat for 3-4 minutes or until smooth.
Remove from the heat & stir in the vanilla
Add the cereal to a very large bowl – I always spray my bowl & pot with non stick spray to help limit the marshmallow sticking as it cools – and pour the marshmallow peanut butter mixture over the cereal; stir to coat evenly.
Spread the cereal into a well greased 13 x 9 inch pan.
Cool completely & then cut into bars. Store in an airtight container.