This Cream of Watercress Soup is a great winter soup for a cold day. Better yet, it's really fast to put together. You can have it on the table in 30 minutes. Watercress has a wonderful, peppery taste and is full of vitamins A, C, and K. Adding the finely diced stalks gives the soup extra flavor, while the butter or cannellini beans give it a higher protein content than the usual potatoes and a creamy texture and taste without dairy. If you cook your own beans, add the liquid they were cooked in and cut back on the stock proportionately. If you aren't vegetarian, try making this soup with chicken stock.