Line a 13x9-in. pan with foil. Butter foil with 1 teaspoon butter; set aside. In a saucepan, combine the sugar, milk, pumpkin, pumpkin pie spice and remaining butter. Cook over medium heat until candy thermometer reads 238° (soft-ball stage), stirring constantly., Remove from the heat. Stir in the chips, marshmallow creme and vanilla until smooth. Stir in nuts. Pour into prepared pan. Cool completely., Using foil, lift fudge out of pan. Discard foil; cut fudge into 1-in. squares. Store in an airtight container.