Cut the cured pork into small cubes. Peel and wash carrots and celery and cut into small cubes. Clean, wash and quarter leek lengthwise and cut into small pieces. Peel and finely dice the onion.
Heat the oil in a pan. Sauté the smoked pork in it for 1-2 minutes. Take out and let drain on kitchen paper. Put the diced vegetables into the pan and sauté for about 1 minute. Stir in tomato paste, roast briefly, then add tomato cubes and stock.
Season the sauce to taste with salt, pepper and a little sugar and simmer gently for about 10 minutes. Grate cheese. Heat crème fraîche and processed cheese in a pot and stir until smooth. Season to taste with salt and pepper.
Grease the casserole dish. Spread some cheese sauce on the bottom. Place 3 lasagne plates next to each other. First put 1/2 of the casserole dish, then 1/2 of the tomato and vegetable sauce, 1/3 of the cheese sauce and again 3 lasagne plates.
Repeat layers, finishing with cheese sauce. Sprinkle the lasagne with cheese. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 40 minutes. Remove lasagne from the oven and garnish with basil.