Wash and Clean beans. Soak beans overnight in water to cover. Add more water if needed. Cook until almost tender. Score salt pork rind, put half the pork with onion bottom of a bean pot and add beans. Mix molasses, mustard and salt with a little hot water and pour over beans. Add just enough water to cover. Place remaining pork on top, cover and bake very slowly 6 to 7 hours. Add hot water occasionally if needed. During last hour, uncover to brown.