Both potato dishes are rich, decadent, and contain cream. However, there are a few distinct differences when it comes to the cooking process. Potatoes Au Gratin are thinly-sliced par-boiled potatoes, baked in cream and topped with cheese which makes the "gratin". Gratin Dauphinoise, is a side dish made of thinly-sliced raw potatoes that bake in cream for significantly longer then Au Gratin Potatoes.