Super Fudge

In a heavy, large saucepan, bring sugar and milk slowly to a rolling boil. Let it boil for no longer than 8 minutes, stirring constantly to keep milk from scorching. Remove from heat and add marshmallows, chocolate chips and butter. Stir until melted and blended in well. Add nuts and vanilla. Spread on a large, ungreased pan, and when cool, cut into squares.