Coarsely chop the onion, then sauté it in the drippings over medium heat until they are translucent. While they are cooking, peel the eggs and slice them, perhaps ⅛ inch thick, and slice the potatoes about ¼ inch thick. Some folks like the potatoes cubed. If you are among them, don't let me talk you out of it. Just keep things bite sized. Set them aside for a few minutes. When the onions are soft and translucent, add the flour, celery seed, mustard seed, pepper, and salt, and cook and stir for about 3 minutes. Add the vinegar, water or broth, and sugar, and stir until it begins to thicken. Add the bacon, eggs, and potatoes. Stir gently to coat everything with the sauce, trying not to break the potatoes and egg yolks too much.