Fans of potato trivia, rejoice! No longer will you struggle to remember the difference between potatoes dauphine and potatoes dauphinoise — or even that there is a difference in the first place.
Because different they are. Quite different, as a matter of fact, despite their similar names. The quick version: potatoes dauphine (pronounced "do-FEEN") = deep-fried potato puffs. Potatoes dauphinoise ("do-fin-WAHZ") = baked scalloped potatoes.
The story begins in the French region of Dauphiné, situated between the Alps and the Rhone Valley in southeastern France.
The name Dauphiné ("DO-fee-nay") comes from the word dauphin ("DO-fan"), the French word for dolphin, owing to the fact that the family who controlled that region, before it became part of the Kingdom of France, had a dolphin on their coat of arms.
Later, it became the custom for the heir apparent to the throne to receive the title of Dauphin, along with rulership of the Dauphiné region. The wife of the Dauphin was called the Dauphine ("do-FEEN"). Therefore, potatoes dauphine (called pommes dauphine in French) are named after the wife of the Dauphin.
The Marie-Antoinette connection makes sense when you consider the fact that pommes dauphine are classic French comfort food — fluffy pillows of mashed potatoes mixed with choux pastry (the kind used for making cream puffs and éclairs), formed into balls and then deep fried until golden brown and cripsy on the outside. Most likely invented by the head chef at the Palace of Versailles. Let them eat cake, indeed.
Potatoes dauphinoise, on the other hand, are named not after a person (or a sea mammal), but after the Dauphiné region itself, where the local cuisine is known, among other things, for featuring a wide variety of gratin-style dishes.
Here in the States we think of a gratin as anything that's baked with a layer of cheese on the top and then browned in the oven — often, but not always, with a topping of seasoned breadcrumbs. To make a potato gratin, we'd probably thinly slice some potatoes, layer them with a mixture of cream, egg and Gruyère cheese and then bake it. The question of whether to use breadcrumbs for the top layer is to some extent a matter of preference, but atop potatoes, they are arguably extraneous.
However... In France, the components of a traditional potatoes dauphinoise (you'll sometimes see it referred to as gratin dauphinois) are subject to neither reinterpretation nor reconfiguration. It's very much a settled question.
Thus a traditional gratin dauphinois will contain neither cheese nor eggs. The starch of the potato, it will be made clear to you, is more than sufficient to bind the dish together. Furthermore, the addition of cheese of any kind will produce a dish that is far too rustic. Peasant fare, you'll be advised. And not in a good way.
Fair enough, though. If you've ever looked at the instructions for making a gratin, you might be struck by the fact that one of the steps is to rub the inside of the baking dish with a clove of garlic. There's no actual garlic in the dish. You just rub in inside the dish before filling it.
The point? The flavor of the garlic is meant to be subtle. Amidst the mild flavors of the potatoes, cream and butter (along with a grating of fresh nutmeg), the garlic makes it presence felt as something of a phantom — a suggestion merely hinted at rather than overtly stated. Even a small amount of cheese, especially one like Gruyére, would drown that out. It'd be like wearing your earbuds at a séance.