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 1.2 litres of 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 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.