Bring 2.5 liters of water to a boil in a large saucepan. Add raw sausages, then diced onions. Then add the stock cubes. Cook everything for half an hour.
Add the kale and cook for another half an hour. Add the potato pieces to the pot. As soon as these are done, remove the sausages and mash the contents of the pot coarsely or finely as required (not with the hand blender! It will be too fine). Put the sausages back in and let them simmer on a lower flame. Then fry the bacon in the butter and add the resulting fat to the saucepan. The bacon is not needed and can be served separately as desired. Season to taste with the spices and soy sauce or Maggi and simmer again briefly.
Note: If you don`t like the Mettwürste, you can also choose to serve boiled Wiener or Frankfurter sausages. The latter, however, are essential for the taste.