Soak the beans (overnight). Place 1 lb dried navy beans in a large bowl, cover with plenty of water, and soak overnight.
Cook the beans (next morning). Drain the beans, add them to a pot of cold water, cover, bring to a boil, then reduce to a gentle simmer for about 1 hour until fork-tender (not mushy). Drain and rinse with cold water; set aside.
Sauté bacon + onion. In a heavy-bottom Dutch oven, sauté ½ lb diced bacon and 1 finely diced onion for about 5 minutes, until the onion is translucent.
Build the sauce. Add salt, pepper, mustard powder, molasses, brown sugar, ketchup, and water to the Dutch oven. Bring to a boil, stirring occasionally.
Add beans. Stir the cooked beans into the boiling sauce, then remove from heat.
Bake low and slow. Cover with a lid and bake at 275°F for 5–6 hours. Stir every 30 minutes, adding a few tablespoons of water if the beans start looking dry.
Serve. Serve hot (and yes—leftovers get even better).