In a heavy skillet, fry the bacon over moderate heat until crisp; place on paper towels to drain and cool. Crumble the bacon and set aside.
Drain the bacon drippings from the skillet, reserving 6 tablespoons. Add the 6 tablespoons of bacon drippings back to the skillet and heat over moderate heat. Add the onions and fry until tender but not brown. Add cider vinegar, sugar, salt, black pepper, dry mustard, and parsley. Bring just to a boil and then remove from heat.
Either use the dressing while it is still hot or reheat if needed.
Makes approximately 2 1/2 cups.
Hot Bacon Dressing Recipe: https://whatscookingamerica.net/salad/hotbacondressing.htm