Set up a double boiler and combine the eggs, sugar and vinegar in the top pan (be careful not to let any boiling water leak into the mixture).

Stir the mixture constantly until it thickens then set it aside and let it cool.

Beat the whipping cream until soft peaks form.

Combine the grapes and marshmallows in a large bowl.

In a separate bowl, mix together the pineapple and the egg mixture and then gently fold in the whipped cream.

Now gently fold the whipped cream mixture into to the bowl of grapes and marshmallows.

Allow the salad to chill for 24 hours before serving.