Place cheese in top of double boiler; bring water to boil. Reduce heat to low; cook until cheese melts, stirring constantly. Melt butter in saucepan over medium heat.
Sift sugar and cocoa together in large bowl. Add melted cheese and margarine to sugar mixture, stirring well with wooden spoon. Add vanilla and nuts; knead until mixture is well blended. Spread in 15x10x1-inch jellyroll pan. Cut into 1-inch squares. Yield: 6 1/2 lbs.