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. Dry onions are fully matured, with juicy flesh and dry, papery skin and have a pungent flavour that becomes wonderfully sweet upon lengthy cooking.

Varieties of onion differ in size, strength and colour. The yellow onion is the most commonly known variety; it has pale golden skin, greenish-white flesh and a strong taste. Red onions are an attractive, milder alternative to the yellow onion with their shiny purple skin and red-tinged flesh. Shallots are a sub-species of onion; they are small and boast a delicate flavour integral to French cooking. Spring onions are immature onions pulled before the bulb is fully formed, and can be recognised by their long green leaves. Like red onions, they are fairly mild and often used raw in salads.

When chopped, onions produce a volatile, sulphur-rich oil that makes eyes water. Over the years cooks have devised many ways to prevent this - freezing the onion; wearing goggles or holding your breath - but they are rarely completely effective. The best way is to not cut through the root of the onion, as this is where most of the oil resides.