Line a 9-in. square pan with foil. Grease foil with 1-1/2 teaspoons butter; set aside. In a large saucepan, melt remaining butter over low heat. Add chips and milk; cook and stir for 10-12 minutes or until chips are melted.
Stir in marshmallow creme and extract; cook and stir 3-4 minutes longer or until smooth. Pour into prepared pan. Chill until set.
Using foil, lift fudge out of pan. Discard foil; cut fudge into squares. Store in the refrigerator.