In a large pot, mix together corn syrup, sugar, and peanut butter. Cook over medium heat, stirring until peanut butter melts. Watch closely at this point. Bring mixture just barely to a boil. (Bubbles should just be beginning to rise. If you boil too much bars with be hard.) Remove from heat, and stir in crisp rice cereal.
Transfer mixture into a well buttered 9x13 inch pan. With your hands well buttered, pat it down into pan.
OPTIONAL: If using chopped peanuts, sprinkle them on the bars as soon as you frost them, before chocolate/butterscotch hardens.