1 Place the stock and the lentils in a pot and bring to the boil. Simmer for 20 minutes.
2 Add the vegetables, potatoes, bay leaf and the thyme and simmer for another 20 minutes.
3 Place the sausages in a metal bowl, cover with boiling water and place a lid on top.
4 Heat some clarified butter and fry the bacon. Add the onion and fry for a few minutes.
5 Season the soup with vinegar, salt, ground black pepper and a few pinches of sugar and stir in the onion-bacon mixture.
6 Slice the sausages, place them in a terrine or in deep plates anad ladle the soup over them. Serve garnished with parsley.