Bean soup is comfort food, especially on a chilly fall or winter day. This soup is prepared and cooked with simple seasonings and a ham bone or diced ham. I add some chopped celery and carrots, but it is very good with just onions as well. The slow cooker makes this bean soup a snap to prepare, and it makes a great meal with hot baked cornbread, biscuits, or freshly baked bread or rolls warm from the oven. Beans are sometimes tough after many hours of cooking. Salt and acidic ingredients can contribute to this problem, so wait until the beans are tender before salting. Some professionals (and food scientists) disagree that salt is the culprit, however, and suggest that brining the beans in salt water overnight cuts down on the cooking time and results in tender beans. See the tips and variations for more about brining.