Question: what is the difference between potato dauphinoise and gratin?
Answer: Potatoes au gratin are slices of pre-cooked (usually boiled) potato cooked in cream and topped with cheese which makes the gratin. Gratin Dauphinoise, on the other hand, is a dish made of thinly-sliced (not pre-cooked) potatoes that cook in cream. Dauphinoise traditionally does not contain any cheese.