Place 1/2 cup miniature marshmallows on a tray or in a shallow pan. Freeze until firm. Place 6 (1 ounce) squares semi-sweet chocolate and 1/2 cup butter in large bowl. Set aside. In heavy saucepan, combine 2 cups sugar, 1 cup miniature marshmallows and 2/3 cup evaporated milk.

Bring to boil over medium heat. Then boil 5 minutes, stirring constantly. Pour over chocolate mixture. Stir until well blended and mixture begins to thicken. Add 1 cup chopped walnuts, 1 teaspoon vanilla and frozen marshmallows. Pour into lightly greased 8 inch square pan. Chill until firm. Cut in squares. Store covered in cool place. Makes 2 pounds.