Clean, wash and cut the leek into rings. Heat the oil in a large saucepan and sauté the leeks for about 8 minutes, turning them over. Season with salt and pepper. Add 1 litre cold water.
Stir in the contents of the bag. Bring to the boil while stirring and simmer at low heat for about 10 minutes. Stir in cream and 100 g cheese. Meanwhile, wash the meat and pat dry. Wash, clean and slice the tomatoes.
Cut the ham slices in half. Place the escalopes side by side in a small fat pan of the oven. Cover with 1/2 slice each of ham and tomatoes. Spread leek cream evenly on top. Cook in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for about 2 hours.
Sprinkle with 75 g cheese 30 minutes before the end of the cooking time. Wash parsley, shake dry, put a small stalk aside for garnishing. Cut the remaining parsley into strips. Remove oven chips from the oven, sprinkle with parsley and garnish with parsley leaves.