Soak the black beans. There are two good options: First, you may place the beans in a bowl and add water to cover by at least two inches. Cover and let stand overnight or up to 24 hours, refrigerating if the kitchen is very warm. Drain well and discard the soaking liquid. Alternatively, for a quick soak, pour boiling water over the beans to cover by two inches. Let stand for at least one hour or up to a few hours. Drain as with the first method.For a slow cooker method: Place the onions, celery, garlic, jalapeño, drained beans, ham hock, tomato paste, and 7 cups of water in the slow cooker. Do not add the sherry, salt, or pepper at this point. Cover and cook on low heat for 7-8 hours or until the beans are tender. You may instead cook on high heat for approximately half the time.For a stovetop version: Heat a tablespoon or two of olive or vegetable oil in a large stockpot over medium heat. Sauté the onions, celery, and jalapeño until tender, about 5-7 minutes, adding the garlic in the last 30 seconds. Add 9 cups of water along with the drained beans, ham hock, and tomato paste, and bring to a boil. Immediately reduce the heat and simmer, partially covered, until the beans are tender, about two hours. (Test the beans after approximately 1 1/2 hours to check for doneness.)For both versions: When the beans are tender, remove the ham hock to a plate, and allow to cool for a few minutes. In the meantime, purée the bean mixture in a blender or with a handheld immersion blender. For ease, I like to use an immersion blender and keep the soup a little chunky. If you are using a blender and prefer not to completely purée the soup, blend half of the soup.Discard the ham bone and any fat, and dice or shred the meat. Return the meat to the slow cooker or pot along with the salt, pepper, and sherry. Cook for a few more minutes to heat through. At this point, if you prefer the soup to be thicker, you may simmer a few more minutes with the lid off. The soup will also thicken slightly as it sits.Serve with toppings of choice.