Open peanut butter (be sure to remove all of the foil seal) place in microwave for up to 2 minutes. Remove and pour into large bowl. Place marshmallow in microwave for 45 seconds. Add to peanut butter in large bowl.
Grease (with butter or margarine) a 13 x 9 baking pan.
Combine water and sugar in medium sauce pan. Place pan on heat. Heat until it comes to a rolling boil. Once it reaches a rolling boil – time for 3 minutes. DO NOT SCRAPE OR STIR AT ANY TIME.
Remove from heat and pour over peanut butter and marshmallow. Mix well and pour into 13 x 9 pan and let set.