Preparation: 10 minutes
Refrigeration: 4 hours
For filling, heat chocolate milk, chocolate pieces and salt over low heat, stirring constantly, until chocolate melts. Add marshmallows; continue to heat and stir until marshmallows are melted. Remove from heat; blend in vanilla. Chill until slightly thickened; fold into whipped cream. Pour filling over crust. Freeze until firm.
Remove from freezer 10 minutes before cutting. Top each serving with additional whipped cream and a walnut half.
Makes 12 servings.