We always have a large quantity of broccoli and cauliflower stalks hanging around from other recipes. I slice off the outer fibrous side of the stems (all the green part for the broccoli) and chop the stalks into ¼-inch chunks. If you do not have leftover stems available, you can add more celery at the end of the cooking process, about 10 minutes before the chowder is done, or you can add chayote, kohlrabi, turnips, yellow beets, or fennel. I find the more vegetables in this soup, the better it tastes. If you’re caught with a bounty of fresh thyme and dill, this soup is also a great way of making use of them.