Combine the vinegar, onion, sugar, mustard and salt in
a bowl and stir vigorously with a wire whisk until the
sugar, mustard and salt dissolve
Whisking constantly,
pour in the oil as a slow, thin stream and continue to
beat until the dressing is smooth and thick
Stir in the
poppy seeds and taste for seasoning.
Serve the dressing at once with any fruit salad or cover
tightly with plastic wrap and store in a cool place or the
refrigerator until ready to serve
Tightly covered and
refrigerated, the dressing can safely be kept for 6 to 10
days
