Drain pineapple, measure 1/2 cup syrup into top of double boiler. Save drained pineapple (2 1/2 cups). Mix eggs, vinegar, and flour into syrup. Stir over hot water until thick. Cool. Beat cream until stiff. Beat in sugar. Fold into cooled egg mixture. Fold in pineapple and marshmallows. Chill overnight. YUMMY!!