Hot German Potato Salad

Cook, peel, and dice the potatoes, keeping them warm in a large serving pan.

Fry the bacon with onion if using, then crumble the bacon over the potatoes.

Leave about 1/2 cup bacon fat in the pan and whisk in vinegar, sugar, flour, salt, mustard, celery seed, and water.

Cook the dressing until thick and glossy.

Pour it over the potatoes, fold gently, and reheat later in a slow 300°F oven if needed.