Soak beans in cold water overnight. Drain.
Cover beans with fresh cold water, par-boil beans. Boil for 10 minutes. Drain, reserving liquid.
Place 3 or 4 slices of salt pork in the bottom of a bean pot, add half the beans, onion and more salt pork.
Cover with remaining beans and 3 slices of salt pork (Ending with salt pork)
Stir together the maple syrup, molasses, mustard and salt. Pour over beans.
Cover bean mixture with reserved bean water.
Bake at 325° for 4 to 6 hours