Not many dishes have a proper birthday, but this classic, of sliced potatoes baked with cream or milk was first officially served in the Dauphinois town of Gap on 12 July 1788 as an accompaniament to the ortolans served by Charles-Henri, Duke of Clermont-Tonnerre.
Unlike many dishes the potatoes are raw, but sliced very thinly and layered in a buttered casserole dish. Many chefs add gruyère, although that officially makes it a gratin savoyard. Don’t confuse it with pommes dauphine.
Other names you may see for the same thing are pommes de terre dauphinoise, potatoes à la dauphinoise and gratin de pommes à la dauphinoise.
Image by GeeJo on Wikimedia Commons