The pancetta and cheese rind give this soup a rich, almost creamy flavor. We removed the stems from the Swiss chard, but if you don't want to waste them, feel free to put them in the soup as well: Once the leaves are sliced, chop the stems and add them to the soup along with the leaves.
Cooks' notes:
·Beans can be soaked up to 12 hours. ·To quick-soak beans: Cover beans with cold water by 2 inches in a 5- to 6-quart pot and bring to a boil, uncovered. Boil beans, uncovered, 2 minutes, then remove from heat and let stand, uncovered, 1 hour. ·Soup is best when made 1 day ahead (to give flavors time to develop). Cool completely, uncovered, then chill, covered. Reheat and, if necessary, thin with water.