2Combine sugar, milk, vanilla and butter in large, heavy saucepan. Bring to a boil, stirring occasionally. Boil for 2 minutes.
3Remove from heat and add marshmallows, semi-sweet chocolate chips, milk chocolate chips and unsweetened chocolate. Stir until melted and smooth. Stir in nuts. Mix well.
4Pour into prepared pans. Let fudge sit at least 24 hours before cutting into squares. Refrigerate for easier cutting.