Peel some very firm potatoes, and slice them into paper-thin slices.
(You ought to be able to see the blade of the knife through each slice.) Grease a fireproof casserole or cast-iron dish with butter, and lay these slices in it, filling the dish only three-quarters full.
Season each layer with salt and pepper.
Now pour just enough milk or cream into the dish to cover the potatoes (or a mixture of milk and cream).
Dot over with butter.
Now simmer over a very gentle heat with an asbestos mat for about 20 minutes, adding a little more milk if necessary; then put into a moderate oven for 35 to 40 minutes.
(In this recipe the ingredients cannot successfully be transferred from one utensil to another.) Do not disturb the potatoes at all.
Cooked in this way in butter and milk (which should boil only very, very gently) the thin slices of potato remain intact and melt in the mouth quite deliciously.
This is the genuine Gratin de Dauphini, which is made unquestionably without either garlic or cheese.