Here’s the converted recipe with USA measurements, resized by 1/2:

• 3.3 lbs potatoes (1.5 kg)
• 3.4 fl oz milk (100 ml)
• Nutmeg (to taste)
• 1 quart heavy cream (1 liter)
• 2 garlic cloves, crushed or finely grated
• 2.6 oz mild cheese (75 g)

1. Preheat the oven to 250°F (120°C).
2. Combine the cream, milk, garlic, salt, pepper, and nutmeg. Whisk thoroughly.
3. Peel the potatoes, then slice them thinly using a sharp knife or mandolin.
4. Rub a 8 x 6½ inch (20 x 16 cm) ovenproof dish with butter. Arrange the potato slices in the dish, adding cream between layers and a little cheese in the middle layer. Press the slices down to ensure they are fully covered in cream.
5. Bake in a water bath (bain-marie) for 2–3 hours, or until the potatoes are tender and the top is browned.

https://www.youtube.com/watch?v=RFMb1xEl6Lw