Cover pinto beans with enough water to cover & bring to a boil. Reduce heat & simmer until they are just tender. Add potatoes, celery & salt & more water if necessary. Cook over low heat. Just before the potatoes & beans are tender, gently fry the onions in a heavy skillet. Using a slotted spoon, add the beans to the skillet & stir until well mixed & heated through. Serve hot over rice or a stiff porridge. *This dish traditionally uses manioc (casava) in place of the potatoes. If you can get it, use it.