Peel, wash and slice or cut the potatoes. Peel garlic and chop finely. Wash thyme and dab dry. Boil potato slices in milk. Simmer garlic, thyme, salt and pepper for about 10 minutes.
Remove the thyme stalks. Lightly grease a baking dish and add the potato-milk mixture. Pour cream balance over it and sprinkle with cheese. Bake in the preheated oven (electric range: 200 °C/ convection oven: 175 °C/ gas: level 3) for 40-45 minutes. In the meantime, clean and wash the lamb's lettuce and mushrooms. Wash the tomatoes, clean the mushrooms and clean them. Cut tomatoes and mushrooms into slices. Mix vinegar and honey and add oil. Season with salt and pepper. Mix lamb's lettuce, tomato and mushroom slices and sprinkle with the vinaigrette.
Wash the tomatoes, clean the mushrooms and clean them. Cut tomatoes and mushrooms into slices. Mix vinegar and honey and add oil. Season with salt and pepper. Mix lamb's lettuce, tomato and mushroom slices and sprinkle with the vinaigrette. Remove gratin from the oven and serve with the salad. Garnish with thyme