Soak the beans overnight in the water. Transfer to fresh water to cover. Bring to a boil and allow to simmer slowly for 1 hr. Drain and reserve the liquid.
Place the beans, salt pork or bacon and whole onion in a large deep casserole or bean pot. Mix the molasses, brown sugar, mustard, salt and pepper with 1 cup of the reserved bean liquid. Stir in beans and add enough bean liquid to cover. Expose only the pork rind on the salt pork and cover the casserole.
Bake in a pre-heated 300 degrees oven for about 2 hours. Add the necessary remaining liquid to cover, stirring well, and cook a further 2-3 hours or until beans are tender. Uncover the beans for the last 30 minutes.
To serve, remove and discard the onion. Remove the salt pork or bacon. Check the seasoning and serve.