Start by preparing the vegetables. Peel the potatoes, carrots, and celery root (if using) and roughly slice them into small cubes. Peel the onion and finely slice it. Cut the leeks into fine stripes. Finely chop the parsley.

Heat the oil or butter in a large saucepan and fry the onions on medium heat until they start to brown for about 5 minutes. Add the potatoes, leeks, root celery, and carrots to the pot and fry for a further 2 minutes.

Pour in the broth/stock and add the bay leaf and marjoram. Cover the saucepan with a lid and leave the vegetables to simmer for around 30 minutes at medium-low heat. Check the soup occasionally and give it a good stir. (I never state the amount of salt, because every broth /stockpot is different. Please season to your personal preference)

Remove the pot from the heat. Check that the vegetables are cooked through and remove the bay leaf. For a creamy potato soup blend with a stand or immersion blender until you achieve a creamy consistency. Stir in the heavy cream or sour cream.

Adjust the seasoning with salt and black pepper to taste. Place the sausages into the warm (no longer cooking soup). The sausages (Frankfurters or smoked sausages such as Mettwurst or Krakauer) just need to be heated up, not cooked. Sprinkle in the fresh parsley just before serving. (For Bratwurst see below)

If you are using bratwurst – then slice the bratwurst into little chunks. Fry in a little oil in a separate pan before adding to the soup.

Serve with some bread. If you would like stir in a spoon of sour cream or heavy/double cream before serving.