Place chocolate chips, marshmallow creme, vanilla and walnuts in a mixing bowl.  Heat sugar, butter and milk in a large saucepan.  Bring mixture to a boil and boil for 15 minutes, stirring often.  Continue to boil until mixture reaches 234 degrees or soft-ball stage on a candy thermometer.  Place mixture into mixing bowl containing chips and beat on high speed until creamy.  Pour into buttered 8" x 8" pan.  Will set in about 3 to 4 hours.