Cut the rind off the bacon. Put both together in a pot and cover with approx. 1 1⁄2 l water. Bring to the boil, cover and simmer for about 45 minutes.
Rinse and drain the lenses. Add bay leaf and lentils to the bacon and bring to the boil. Cover and simmer for about 45 minutes.
Peel, wash and chop the carrots, celery and potatoes. After about 15 minutes add to the lentils and cook. Clean, wash and chop the leek.
About 15 minutes before the end of the cooking time, remove the bacon and cut into cubes. Cut mettenden into pieces. Add bacon and leek to the stew and finish cooking. Remove the bacon rind. Season the stew with marjoram, salt, pepper, 1 pinch of sugar, vinegar and mustard