This is a recipe which my mother used to make, she was originally from Silesia which was taken over by Poland after the last war:
Boiled potatoes hard boiled eggs onions mustard salami oil and vinegar Beef stock or a stock cube Mustard
Boil the potatoes and cut them into chunks. Pour over beef stock and leave to cool. Add half a cup of oil and half a cup of vinegar and add the hard boiled eggs and sliced onion. Then add finely sliced salami and some mustard.