Clean, wash and chop the leek. Peel, wash and dice carrots, celery and potatoes. Heat 1 tablespoon of oil in a saucepan and sauté the vegetables in it. Deglaze with 1.2 litres of water.
Add the meat, bay leaf, peppercorns and thyme and cook over medium heat for about 30 minutes. In the meantime peel onions and cut them into rings. Leave the bacon in a pan until crisp. Drain on kitchen paper and crumble coarsely.
Heat 2 tablespoons of oil in a frying pan and fry the onion rings until golden brown. Take the meat out of the soup and dice it. Mash a part of the soup. Add the diced smoked pork. Season soup with pepper, 1 pinch of sugar, some salt and oregano.
Arrange the soup in deep plates, sprinkle with onion rings and bacon pieces. Serve garnished with oregano.