Rinse the beans thoroughly and soak them in 2 inches of cool water for at least 4 hours, or ideally overnight, until they have doubled in size.

Drain the soaking water and move the beans to a pot with fresh water to cover. Bring to a boil, then simmer gently for about 1 hour until tender. Once soft, stir in the salt and let them stand in the cooking water for 30 minutes to absorb the flavor.

Drain the beans but keep 1 cup of the cooking water. In the same pot, heat the oil over medium heat and sauté the onions until they soften and begin to brown, about 5 minutes. Stir in the turmeric for 1 minute.

Add the beans and the reserved cooking liquid. Simmer for 5 minutes until the sauce thickens and coats the beans; it's okay if some beans fall apart as this adds to the creaminess.