1. Rinse beans. Soak overnight in about 1 quart water in a medium pot.
2. Discard soaking water. Pour in about 1 quart new water, and all remaining ingredients.
3. Bring to boil. Reduce heat to very low. Cover and simmer 1 hour.
4. Remove lemon, leaf, and chile. Use back of a spoon to mash 10% of the beans against inside of pot. Cover and simmer 45 minutes more.
5. Remove cover. Simmer to reduce water until soupy, about 15 minutes.
6. Serve hot in small bowls as a side dish or snack. Good with eggs, tortillas, or other Mexican food. Leftovers keep well in the refrigerator.
Use dry beans, not canned. Amazingly cheap, they have a much better texture and more flavor.
The preserved lemon piece is notably better than fresh lemon. Keep them on hand: they are very very simple to make, and a wonderful seasoning for many dishes. If you must, substitute fresh whole lemon plus t salt.