Scalloped Potatoes

A quarrel rages in France as to what may be the true gratin dauphinois. Egg and cheese are included in the recipes from old cookbooks (too far removed from the sources, according to the purists). Nearly every reputed restaurant has its celebrated gratin dauphinois and each is willing to divulge its recipe, usually incomprehensible and conceived in the interest of mystification (I have eaten potatoes boiled in milk and dryly reheated days later under a salamander in a restauran