How to Make It
In a large pot, combine the beans with enough water to cover by 4 inches. Add the halved onion and the garlic and bring to a boil over moderately high heat. Reduce the heat to low and simmer until the beans are very tender, about 2 hours. If the beans are soupy, strain them and reserve the cooking liquid for another use. Discard the onion and garlic and season the beans generously with salt. Ladle into bowls, garnish with diced onion, tomato, cilantro and jalapeño and serve.