Rinse
scallops well under cold water. Heat wine, water, parsley and onion to
boiling. Add scallops and simmer 5 minutes. Drain. Cut any large
scallops in half. Cool. Sprinkle with 1 tbsp lemon juice and tarragon
vinegar. Cover and chill well, stirring occasionally. Cut hard-cooked
eggs in halves. Lift out yolks and press through a fine sieve. Add
mustard, salt, pepper and tarragon. Add oil and lemon juice drop by
drop, blending well. Stir in finely-chopped egg whites, capers and
parsley. Put scallops in sherbet glasses lined with lettuce. Spoon sauce
over.