Rinse the beans in cold water and drain. Place them in a big heavy pot and cover with enough water to come up to at least 3″ above the top of beans, about 10 cups of water. Incorporate the onion and bring to a boil. Let the beans simmer, partially covered, for about 1 1/2 hours, until the beans are soft and then add the salt. Don’t add the salt in the beginning or it will toughen the beans.

Let them continue simmering, for about another 15 minutes, or until the beans are so soft they come apart if you hold one between your fingers, and the broth has thickened to a soupy consistency. If the beans are not yet soft and the broth is drying out, add more water. Before eating, remove the cooked onion with a slotted spoon.