Line a 13-in. x 9-in. pan with foil and grease the foil with 1 tablespoon butter; set aside. In a large saucepan, combine the sugar, milk, pumpkin, cinnamon, nutmeg and remaining butter. Bring to a boil over medium heat, stirring constantly. Reduce heat; cook until a candy thermometer reaches 238° (soft-ball stage), stirring occasionally.
Remove from the heat. Stir in chips until melted. Stir in marshmallow creme, pecans if desired and vanilla. Spread into prepared pan. Cool to room temperature; cover and refrigerate. Using foil, lift fudge out of pan. Discard foil; cut fudge into 1-in. squares.