Line a 13-in. x 9-in. pan with foil and grease foil with 1 tablespoon butter; set aside. In a saucepan, combine sugar, egg nog, heavy cream and remaining butter. Bring to a boil over medium heat, stirring constantly. Reduce heat. Cook until candy thermometer reads 238 degrees, stirring occasionally.
Remove from heat and stir in chocolate chips until melted. Stir in marshmallow creme, walnuts and vanilla.
Spread into buttered pan. Cool to room temp. Using foil, lift fudge out of pan. Cut fudge into 1-in. squares. Store in an airtight container in refrigerator.