The humble onion is as indispensable to the culinary arts as butter or eggs — or for that matter, knives or plates. It's the rare food that can be sweet, savory, pungent and aromatic all at the same time, but that's what onions do. In a real sense, onions are what make food food — going beyond mere sustenance and making it enjoyable. Making it taste good. Onions don't contribute much in the way of nutrition. The odd vitamin and mineral, sure, but nothing that isn't far more abundant in other commonly available foods like rice or broccoli. Nor are onions functionally necessary for any recipe. If you took them away, everything would still work, it just wouldn't taste as good.