Put broth in a pan on mediuum heat, when it comes to a boil add the finely chopped onion, oil, vinegar and sugar.
Boil until the onion is tender, menawhile slice potadoes in thin slices and put them into a bowl.
Pour the broth over potadoes, mix well with a spoon and season with salt and pepper.
Add the chopped chives.You can eat it immediately or, and I find this far better, let it cold well then eat with a lot of nurnbergwurst