Onions are endlessly versatile and an essential ingredient in countless recipes. Native to Asia, these underground bulbs are prized all over the world for the depth and flavour that they add to savoury dishes. When chopped, onions produce a volatile, sulphur-rich oil that makes eyes water. Over the years cooks have devised many ways to prevent this. The best way is to not cut through the root of the onion, as this is where most of the oil resides.