Step 1Place the beans in a bowl, add water to cover generously and let soak overnight.
Step 2The next day, drain and rinse the beans. Place them in a large saucepan or Dutch oven and add the ham hock and 6 cups of water. Bring to a boil, reduce the heat and cook the beans, partially covered, until the skins wrinkle, about 1 hour. Using a slotted spoon, lift the beans into a large crockery bowl or deep casserole. Reserve the cooking liquid. There should be about 3 cups. Lift out the ham hock. Remove the skin and fat and cut the meat into bite-size pieces. Add the ham to the beans.
Step 3Heat the oven to 325 degrees.
Step 4Combine the brown sugar, molasses, mustard and salt in a small bowl. Add 1/2 cup of the reserved liquid and stir until the seasonings are dissolved and blended. Pour this over the beans and ham. Peel the onion. Cut off the top and root ends but leave the onion whole. Stick the cloves into the onion, and bury it in the beans. Add the remaining cooking liquid to the beans. Cover and place them in the oven. Bake 2 hours, checking the oven temperature after 30 minutes; if the beans boil too hard, reduce the heat. If the liquid is not simmering, increase the heat to 350 degrees.
Step 5Remove the beans from the oven and lay the bacon slices over the top. Increase the heat to 350 degrees, return the beans to the oven and bake uncovered 2 hours longer. Add water if the beans should become too dry. The beans should be juicy but not wet. Taste and add more salt if needed. Accompany with a plate of tomato slices.