The first step in making Grandma Brown's Baked Beans is to soak the navy beans overnight. Rinse the beans in cold water, then place them in a large pot or bowl and cover with water. Make sure there's enough water to cover the beans by a few inches. Cover the pot or bowl and let the beans soak overnight.
The next day, drain the beans and rinse them with fresh water. Place the beans in a large pot or Dutch oven and cover with 8 cups of water. Bring the water to a boil, then reduce the heat and let the beans simmer for 1 to 1 1/2 hours, or until they are tender but still hold their shape.
While the beans are cooking, cook the bacon in a large skillet until it is crispy. Remove the bacon from the skillet and let it cool on a paper towel-lined plate. In the same skillet, sauté the chopped onion until it is soft and translucent.
In a bowl, combine the brown sugar, molasses, ketchup, Worcestershire sauce, dry mustard, salt, and black pepper. Mix well.
Once the beans are tender, drain them and add them to a large baking dish or Dutch oven. Add the sautéed onions and crumbled bacon. Pour the sauce over the beans and mix well.
Preheat the oven to 350°F. Cover the beans with a lid or aluminum foil and bake for 2 to 2 1/2 hours, or until the beans are thick and the sauce has caramelized.
Remove the beans from the oven and let them cool for a few minutes before serving. Garnish with additional bacon or chopped parsley, if desired.