Slice cabbage paper thin, and toss lightly with sugar, shredded carrots. Sprinkle with salt and pepper and drench it all with milk. Cover and refrigerate for about 15 minutes. Meanwhile, combine mayonnaise (not salad dressing), buttermilk, celery seed, Tabasco and minced onion. Mix well with cabbage mixture. Refrigerate again at least an hour before serving. Drain some of the dressing first and serve it separately at the table. It keeps for 24 hours only!!