Peel the potatoes, rinse them, cut them into slices as narrow as possible (ideal: about 1 mm) and dry them on a dish rack (do not soak the potatoes!).
Boil butter, cream, milk, the pressed garlic clove and the spices. Butter a shallow ovenproof dish. Layer the potatoes, spreading them as thinly as possible – the gratin tastes so much better! It may be advisable to use two molds.
Pour the seasoned cream-milk mixture over the potatoes, put the pan in the oven heated to 120 °C (middle shelf) and cook for 2 hours. During this time, the gratin will have turned a golden yellow color. However, if contrary to expectations it browns too quickly, aluminum foil will protect it from further browning.
The gratin can be kept warm in the stove at 50 °C for up to one hour. To prevent it from drying out during this time, place aluminum foil over the dish. For variety, you can put carrots and celery slices between the potatoes, or make it precious with a few truffle slices.
Tip: Stock up on a variety of high-quality spices – it pays off!