Grate the onion on the sugar and allow to stand for 30 minutes. Add the salt, celery seed, and lemon rind. Beat in oil, then vinegar, a little at a time, alternately, until the dressing is very thick. Use with tossed greens salad, cabbage and Roquefort; head lettuce with hardcooked egg, parsley, and crumbled American cheese. This dressing can be made very quickly if you use a blender.