Line a 13-in. x 9-in. pan with foil and grease the foil with 1 teaspoon butter; set aside.
In a large heavy saucepan, combine the sugar, cream, cocoa, corn syrup, salt and remaining butter. Bring to a boil over medium heat, stirring until sugar is dissolved. Cook over medium-low heat, without stirring until a candy thermometer reads 234° (soft-ball stage). Remove from the heat; stir in the marshmallow creme, peanut butter and 1 package chips.
With a hand mixer, beat until mixture begins to lose its gloss, about 6-8 minutes. Fold in remaining chips. Pour into prepared pan. Refrigerate for 2 hours or until firm.
Using foil, lift fudge out of pan. Discard foil; cut fudge into 1-in. squares. Store in an airtight container.