THE ONION WAS FASHIONABLE in the culinary world for a while. Chefs were filling jars with colourful pickled or marinated onions, and it seemed they were serving every other meat dish topped with a big blob of caramelised onion, onion confit, onion marmalade or onion jam. When these four preparations began appearing on menus, many people were surprised to find the familiar sharp taste and biting odour of raw onion could be made into something rich and sweet by cooking it long and slow. Professional chefs and skilled home cooks have known for ages that onions have gentle qualities when 'sweated' over a low heat with a little liquid or fat. But until the onion started making its starring appearances, it had always been a supporting ingredient, not one to brag about. It was diced small and simmered into sauces so its presence could go undetected. When served raw, it was an ingredient to be avoided if the diner had an important outing coming up - onion breath is not an attractive feature on a date or during a business meeting. Chinese and many other Asian cuisines use the young, immature 'spring' or 'green' onions, which are long and thin with a white base and green top. Some people throw away the top but the entire vegetable is edible. These spring onions are sliced and used in stir-fried dishes, finely chopped and mixed with salt and oil for a dipping sauce, or julienned and 'sizzled' with hot oil for seafood. The taste is mild and sweet, even when raw. If allowed to mature, green onions develop a large, round base with juicy flesh and papery skins. There are many varieties, in different colours and shapes. All onions have a natural sweetness, but with most varieties this characteristic is brought out only by cooking. Other varieties are sweet even when raw, and in fact, cooking them makes them lose their sweetness. When buying onions look for firm flesh with no bruises or soft spots, which can develop into a disgusting, smelly, black mould. A major problem with onions is that when cut, they release a volatile compound that irritates the eyes and causes most people to 'cry'. People who wear contact lenses or glasses don't have this problem because their eyes are protected by the lenses. If you find slicing onions troublesome, try chilling them in the fridge (which suppresses the compound), or rinse away the compound by running the sliced onions under cold running water.