Watercress is often passed by in the produce aisle in the pursuit of baby arugula, its closest flavor kin, but it's just as (or even more) peppery tasting and can hold its own when heated. Here the tender leaves are showcased in a creamy soup that gets it's creaminess from being pureed, with zero actual cream being necessary. Of course, the potatoes are what lends the soup its body (thanks to the natural starches).