Mix 20 cl of milk with 20 cl of Cream. Season with salt, pepper and nutmeg, and stir until you obtain a smooth mixture suitable for topping. Add a peeled garlic clove. Bring to the boil.
While the mixture is heating, cut the other garlic clove in halves and rub it vigorously onto the gratin dish, then grease the dish using a brush and melted butter.
Peel 800 g of Charlotte potatoes, rinse, then keep in cold water to prevent them from going black.
Cut them into 5 mm slices using the mandolin and keep any stray pieces, as we can use them later in the recipe.
Remove the garlic clove from the milk-and-cream mixture.
Lay out the round slices of potato on the gratin dish in a rosette pattern. Pour some of the cream-and-milk mixture over the potatoes, then cover with another layer of potato slices, then the rest of the mixture.
Place in the oven for 45 minutes at 180°C.
Check progress using the point of a knife: the gratin should be crispy golden brown on top and soft inside.