Butter sides of heavy 3-quart saucepan. Add 4 cups granulated sugar, one 14 1/2 ounce can (1 2/3 cups) evaporated milk, and 1 cup butter.
Cook over medium heat to soft ball stage (236*), stirring frequently.
Remove from heat; add one 12-oz pkg. (2 cups) semisweet chocolate pieces, 1 pint marshmallow creme, 1 tsp vanilla, and 1 cup broken walnuts.
Beat till chocolate melts. our into buttered 13x9x2 inch pan. Score while warm, cut when cool and firm.