In 2 qt. glass measure, combine marshmallows, milk, and salt. Microcook on HIGH 3-4 minutes. Stir until marshmallows melt and mixture is smooth. Add chips and stir until melted. (If you don't use marshmallows, melt chocolate chips in the condensed milk. Add salt.) Stir in nuts and vanilla. Line 8 or 9 inch square pan with wax paper. Spread fudge evenly in pan. Chill 2 hours, until firm. Turn on to cutting board, peel off paper and cut into squares. Serves 32