An essential kitchen vegetable, onions are arguably the world’s most widely used ingredient. They vary in shape and colour from flattish brown to round pale bulbs but share a common structure, with a papery outer skin and protecting inner layers of pale, crisp flesh. Yellow onions are hot and pungent enough to make your eyes water; Spanish onions are the largest, with brown skin and a mild, sweet flavour; brown onions are a smaller variety of yellow onion with an even more pungent flavour, making them a good all-rounder.
Onions are available all year. Main crop British onions are available fresh from the fields in August and September, and from cold storage until the following July.
Choose onions that are firm and regular in shape, with tight, dry, papery skins. Avoid any with shrivelled skins or any that feel soft around the neck or are sprouting green shoots. If possible, select individual bulbs when shopping, rather than buying them ready-packed.
Onions store well, especially if kept in a cool, airy larder or shed. Ideally they should be tied on a string or raffia rope and hung somewhere cool and dry. Otherwise, store them in a paper bag in a vegetable rack for up to ten days. Keeping them in the fridge will cause them to soften.
Peel and chop onions before freezing them in convenient portion sizes. They will be a little mushy when defrosted because of their water content, but can be cooked from frozen in soups, stews and casseroles.
Onions can be used as flavouring or as a vegetable in their own right. They can be fried, boiled, roasted, grated and sautéed, or used as a classic ingredient in dishes such as onion soup, onion tart, onion marmalade and Spanish tortilla.