Rinse beans, add to a pot and add 6 cups of water. Bring to a boil and hold for 2 minutes. Turn off heat, cover, and let stand 1 hour.
Add 1 teaspoon salt to the pot and stir in, place back on heat and simmer, covered, for 1 hour or until beans are tender.
Drain beans, reserving the liquid. Measure 1¾ cups bean liquid, add water if needed, and place in a bowl. To the liquid, add the brown sugar, 1 teaspoon salt, dry mustard, and molasses. Stir together to make a sauce.
Preheat your oven to 150° C (300° F), get out a 2 quart casserole dish with cover or foil.
To the casserole, make layers, add ½ the beans, ½ the onion slices, ½ the salt pork, and ½ the sauce. Repeat the layers ending with sauce.
Cover and bake for 5-6 hours, adding more liquid if needed as beans bake.
Serve and enjoy.