Preheat the oven to 175 °C (convection). Wash and peel the potatoes, then cut them into thin slices (about ⅛ to ¼ inch / 3mm to 6mm thick ) using a knife or mandolin.
Peel the garlic clove, split it lengthwise, and rub it around the inside of a casserole dish. Use half of the butter to grease the inside of the dish.
In a bowl, combine the cream and milk. Arrange half of the sliced potatoes in the casserole dish. Pour in half of the milk-cream mixture and season with a pinch of fleur de sel, a couple of grinds of pepper, and 3 generous pinches of freshly grated nutmeg.
Add the remaining potatoes, followed by the rest of the milk-cream mixture. Season again with salt, pepper, and nutmeg. Cut the remaining butter into small pieces and sprinkle them over the top. Bake for 1 hour and 30 minutes. Enjoy!
