Butter square 7"x7"x2" or 8"x8"x2" pan. Heat chips, corn syrup, peanut butter, vanilla in a 2 quart saucepan over low heat, stirring constantly until chips are melted and mixture is smooth. Remove from heat.
Stir cereal (nuts and raisins if using). Press evenly in pan using the back of a buttered spoon.
Cover an refrigerate about 2 hours or until firm.
Cut into 2" squares. Keep cool. Makes 16 squares. Enjoy!