NOTE: Use navy beans, California pea beans, or small white beans. Soak beans overnight. In the morning, preheat oven to 325degreesF Place the baking soda in a Dutch oven and fill half way with water. Bring to a boil, add the beans & boil for 10 minutes. Drain beans in a colander and run cold water through them. Set aside. Dice the salt pork (available in the bacon section of the grocery store)into 1-inch squares. Put half of the salt pork on the bottom of the bean pot, along with the onion. Put beans in the pot. Put the remaining salt pork on top of the beans. Mix the sugar, molasses, mustard, salt and pepper with 3 cups of hot water and pour over the beans. Cover pot with lid and place the pot into the preheated oven. Bake for 6 hours. Check pot periodically to make sure the amount of liquid is okay. Add water to the beans slowly as needed to keep them moist; DO NOT FLOOD THEM. Just "top them up". Remove the pot from the oven and serve. NOTE: The Durgin-Park, a Boston restaurant whose origins date back to the American Revolution, is famous for its Boston baked beans, baked Indian pudding and apple pan dowdy. Durgin-Park cook Tommy Ryan has prepared this recipe at the restaurant for the past 37 years. Durgin-Park serves 1,000 diners on an average Saturday evening. The waitresses have a reputation for their long memories: the second time you come in, you get the same thing you ordered the first time--unless you speak fast.