This makes a gob of dressing - so unless you are feeding about 40 people, I would recommend cutting these proportions in half. Still, very tasty! And a nice variation from simple oil-and-vinegar based dressings.
1/4 c sugar
1 T Dijon-style mustard
2/3 c red wine vinegar
1/2 tsp salt
3 T yellow onion, grated
2 c corn oil
3 T poppy seeds
Combine egg, sugar, mustard, vinegar, salt, grated onion (and juice) in a food processor. Process for 1 minute.
With the motor running, slowly add the oil in a steady stream. When oil is incorporated, shut motor off and adjust seasonings.
Transfer mixture to a bowl or jar. Stir in poppy seeds. Refrigerate until ready to use.