Peel and wash the potatoes and slice or cut them into fine slices. Grease an ovenproof dish and layer the potato slices in it. Season with salt, pepper and nutmeg. Pour cream over them.
Bake in the preheated oven (electric oven: 200 °C/ gas: level 3) for about 45 minutes. Clean, wash and slice the tomatoes and courgettes. After 20 minutes spread on the potatoes, season and continue baking.
Cut pork fillet into 8 slices. Heat the oil in a pan and fry the meat briefly on both sides. Season with salt and pepper. Wash the basil, dab dry and cut into strips.
Coarsely grate the cheese. 5 minutes before the end of the cooking time of the gratin, add fillet slices, basil and cheese and gratinate.