Peel and slice the onions. Cut the sausage into fine strips (if you don`t get salami, use a similar sausage). Sweat both in oil and butter or margarine until golden yellow. Grate the apple (Granny Smith, Jonagold or a similarly sour variety) with the drop slicer and add a pinch of salt, a little sugar and half a tablespoon of vinegar to the onions. Top up with the meat stock, season with a little salt and cook the onions almost until soft.
Halve the rolls lengthways and fry them in a little melted butter until crispy. Add to the soup.
Serve the soup sprinkled with the grated cheese and chopped parsley just before serving.