Peel and wash the potatoes, dab dry and cut into wafer-thin slices. Clean the zucchini, wash, grate dry and cut diagonally into thin slices. Season cream with salt, pepper and nutmeg.
Peel the garlic Grease an ovenproof dish (22 cm Ø) and rub with garlic. Layer potatoes and zucchini in the dish. Pour cream over it. Spread the fat in flakes evenly on the ingredients.
Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 30-35 minutes until golden brown. Wash thyme, shake dry and garnish gratin with it.