Potatoes, onions, cider vinegar, sugar, corn oil, salt, pepper.
Now this I would like to try....
More often than not I use a 5 pound bag of russets. Boil, dump in cold water, peel, slice. Slice up a big yellow onion, I like pickled onion. 1/2 C cider vinegar, 1/2 C sugar, up to 1/2 C corn oil. I don't like oil that much. Salt an pepper to taste. Best if left overnight or at least a few hours with an occasional stir. Crumbled bacon a good option.
This is a recreation of my grandmother's recipe, she was from Croatia. Since have had the same stuff in a German restaurant. Which figures as Austria once controlled Croatia. In fact one reason my grandfather emigrated was to avoid being drafted into the Austrian cavalry - Austrians thought Croats were naturally good with horsed.
----------------------------------------
Sometimes I'll add a little more sugar if I have the taste for it. But equal parts is a good balance. Cooking the potatoes just right is the trick. Gotta catch them when they're just done or they want to mush more than slice. I don't remember Gramma having that problem, I think it was the heirloom potatoes Grampa grew.