There are endless recipes and options when it comes to making watercress soup, a light or creamy dish in which spicy watercress is the main ingredient. No matter what recipe you choose, some good tips for making this dish include removing the stems from the watercress and waiting until the soup is almost finished cooking before you add it to the rest of the ingredients. To protect yourself from injury and your counters from a mess, puree the soup in batches in a blender or use an immersion blender when following recipes that call for this step. Oftentimes, recipes suggest a small amount of heavy cream, often to balance the spiciness of the watercress; however, this ingredient should always be added just before the soup is taken off of the heat.
Watercress stems leave much to be desired when it comes to texture, often being tough, which is not usually desired in a soup. Even if you plan to puree everything together, it is still advised that you remove the thickest part of the stems before cooking with them. If you are making a watercress soup that does not call for blending, use only the leaves and the thin stems close to the base to maintain the texture and palatability of the dish.
As with any soup in which delicate greens are used, one of the best tips for making the watercress version is to add the main ingredient at the very end of the cooking time. In order to achieve the best flavor, the stock and other ingredients should be allowed to simmer together, yet the length of time needed for this step in most recipes can turn fresh watercress into mush. For this reason, the watercress should only be added when there is about five to seven minutes left in the cooking time if you are only simmering the soup, or three to four minutes if the recipe calls for bringing it to a boil.
Some of the most popular types of watercress soups are the pureed varieties, in which all of the ingredients are blended together to create a thick, creamy dish. Blending hot soup, however, can be both dangerous and messy. If you are using a blender, it is best to puree the soup one ladle-full at a time, even if it looks like there is plenty of room. When overfull, the hot soup can burn your hand as you hold the lid on the blender or cause the lid to pop off entirely, sending the watercress soup all over your kitchen. Ideally, an immersion blender should be used, as this allows you to blend everything at once in the same pot in which it is cooked.
An extremely popular addition to watercress soup is heavy cream, although the timing for adding this ingredient is crucial. Naturally slightly sweet, heavy cream can help to balance the spiciness of the watercress and other peppery ingredients, such as horseradish. Despite this, cream should never be boiled when add to the soup, as the heat can scald it and ruin its flavor. Instead, make sure to add it either right before or right after you take the watercress soup off of the heat. The soup will still be warm enough to heat up the cream, yet not too hot enough to burn it.