Line a 13x9 inch pan with aluminum foil, allowing excess foil to hang over both ends. Grease generously.
Add sugar, margarine and evaporated milk to a medium size saucepan. Heat over medium heat, stirring constantly.
Bring the mixture to a rolling boil for 5 minutes; continue to stir constantly. Remove from heat.
Stir in chocolate chips until completely melted. Add marshmallow cream, walnuts and vanilla. Stir until completely incorporated.
Working quickly, pour into the prepared 13x9 inch pan. Let cool completely before cutting, several hours if possible.