White Bean and Ham Hock Soup with Arugula and Corn Bread Croutons

Soak beans in cold water to cover overnight (8 hours). Drain and rinse well. Simmer ham hocks in 6 cups water in a 3-quart saucepan, partially covered, skimming foam as necessary, 1 hour. Reserve 4 cups cooking liquid and drain ham hocks. Heat bacon drippings in an 8-quart heavy pot over moderate heat until hot but not smoking, then cook onion and garlic, stirring, until softened. Add tomatoes and thyme and cook, stirring, 1 minute. Add soaked beans, broth, ham hocks, and reserved cooking liquid and simmer, covered, stirring occasionally, until beans are tender, about 1 hour.