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

Makes 2-1/2 cups