Wash the porcini and soak in cream. In the meantime clean and wash the zucchini and cut them into thin slices. Peel and wash the potatoes and slice them thinly. Layer zucchini and potatoes in scales in a flat, ovenproof dish.
Cut the mozzarella into slices and spread on top. Season mushroom cream with salt, pepper and thyme, pour over the vegetables. Bake gratin in the preheated oven (electric cooker: 200 °C/ gas: level 3) for about 40 minutes.
These are accompanied by lamb chops fried in olive oil and tomato quarters tossed in the cooking fat. Serve everything garnished with thyme.