What Is Leek Soup?

Leeks are an edible allium plant, a member of the onion and garlic family. Instead of forming a tight spherical bulb like the onion, however, leeks develop into a long tall cylinder of tightly bundled leaf sheaths. The portion normally eaten is its lower stem or stalk, pale white in color. It is cooked in many various ways, but the classic preparation to highlight its mild flavor is leek soup.

Leeks are believed to have been cultivated since ancient times. Archaeological evidence suggests that they were a part of the Egyptian and Mesopotamian diet as early as 2,000 B.C. First century A.D. Emperor Nero of Rome is said to have favored leek soup for its professed medicinal benefit to throat and voice. The ancient traditions of the humble vegetable have survived to modern times as one of the national symbols of Wales, and to a lesser degree the United Kingdom.

Compared with onions’ sharp, sulfurous smell and taste, leeks are more subtle and sweet, though unmistakably a type of onion. Their upper, dark green leaves are fibrous and tough; these are usually discarded, though sometimes used to flavor a soup stock. The white base and lighter green parts of the stalk are also used as an ingredient in soups. True to the traditions of the British islands, potato and leek soup is an especially popular combination.

Leeks grow quite slowly; harvest season is typically late summer to late autumn, after a year and a half of growth. They thrive best in muddy sand, and should therefore be well-washed for cooking. After its leaves and stubby root are trimmed, the tubular vegetable is cut in half lengthwise, so that its tightly layered sheaths can be separated to be thoroughly rinsed. Chopped into thin slices and consumed raw, it is firm and crunchy with a taste some people have described as somewhere between a sweet onion and cucumber.

There are many ways of cooking leeks. Simply grilling or roasting them is popular. Like miniature onion rings, they are fried with a coat of flour or batter. When steamed, boiled or braised, leeks soften and become even more mild in taste. Using these slow-cooked methods, there are several variations of leek soup.

The basic vegetable soup includes leek, and usually carrots and celery. Leek soup is also paired with many other vegetables, such as kale, broccoli or squash, but none more commonly than the potato. Variations of this pairing are found throughout the world, often with additional regional flavors. Cream is often added, or the potato and leek mixture might be thickened with a blender or food processor to a smooth puree texture. Vichyssoise is a chilled, cold soup version of the latter, served with a finishing swirl of evaporated milk.