It can be easy to make a simple leek broth by boiling the leeks in water, but there are some tips that can help when preparing it. Leeks should always be cleaned thoroughly before being used, because dirt and grit can ruin the smooth texture of a leek broth and cause the color to be murky or grayish. Although a broth can be made with just leeks, many times the delicate flavor of the leeks can be enhanced by the judicious addition of other vegetables and aromatics. For the purposes of presentation, a leek broth can be finished in a number of ways, including straining or processing with a blender to get a more distinct texture. The flavor of leek broth also can be adjusted by roasting or otherwise cooking the leeks and any other ingredients before adding them to the broth.
A leek grows by forming layers as it matures, eventually building up the onion-like structure of the stem, leaves and bulb. Dirt, sand, insects and other grit can get between the leaves and can be difficult to remove. To properly clean a leek, it should be cut lengthwise and placed under running water until the layers separate or placed in a bowl of water to allow the dirt to sink to the bottom of the bowl. Removing the dirt can help to make a broth that is clearer and does not have any off tastes from stray soil particles.
Some recipes add vegetables and other aromatics to leek broth, although this must be done in the correct proportions so the taste of the leeks is not overpowered. Garlic, ginger, parsley, carrots and small amounts of celery are all suitable additions that will complement the flavor of the dish. Onions can be used in the broth, although their taste can sometimes dominate the broth and eclipse the more subtle character of the leeks. Additionally, the broth can use water as a base liquid, although chicken or vegetable stock can be used so there is an underlying richness even before the leeks are added.
Once leek broth has finished cooking, some presentations call for it to be clarified. This can be done by straining out all the solids, leaving a translucent liquid behind. In some instances, the ingredients might have caused the broth to become cloudy, in which case egg whites can be added to the hot broth to capture some of the particles and then strained out to help clear the liquid. Another way to create a leek broth with a consistent appearance is to add a small amount of heavy cream and then puree the broth and all its ingredients until it forms a smooth, rich liquid.