For the sour sausage, remove the skin from the extra sausage, cut into thin oblong slices and place in a deep dish. Make a marinade of vinegar, oil, salt, pepper, sugar and water and spread it over the sausage.
Chop the onion very finely and spread it as well, then mix the sausage well with the marinade and the onion. Serve the sour sausage with toasted brown bread or fresh salt sticks.