Soak the beans in cold water to cover overnight.

Preheat the oven to 300F.

Drain the beans.

Combine the beans in a 2 1/2-quart bean pot or covered casserole with maple syrup, brown sugar, molasses, mustard, salt, and pepper.

Add the onion and salt pork.

Pour enough boiling water over the beans to cover them by 1/2 inch.

Bake, covered, for 6 hours, or until the beans are almost tender.

Check every hour and add more boiling water to cover the beans if the sauce level is low.

Uncover and finish cooking for an additional 45 to 60 minutes, until the beans are tender and a rich brown and the sauce is lightly thickened.