I suspect that it's probably going too far to say that the culinary world is riven when it comes to the perfect dauphinoise, but there is enough disagreement as to cooking technique and ingredients to warrant Forkful adding its two penneth to the topic. My standpoint is informed, as with so many things in the kitchen, by my mother's tried, tested and much complimented way of doing things (see below).
Potato dauphinoise is surely one of the most delicious things to grace a table. But before I let you into the best way of cooking it (in my opinion), let's just consider some of the options available. Nigella Lawson, in How to Eat, advises cooks to simmer the potatoes in the milk and cream mixture on the hob before tipping the whole lot into an oven-proof dish and baking. Any number of cooks will tell you to add Gruyere or Parmesan, either to the milk and cream mixture, or to the top layer to ensure a burnished crust. James Martin even advocates mozzarella which I think sounds revolting. Then there's the vexed question of whether to add nutmeg or not. Gordon Ramsey does not; Skye Gyngell, writing recently in the Independent, does. The one thing that seems to unite writers is that dauphinoise is best when large potatoes of the waxier variety are used. Desiree is a popular choice.
It's my view that potato dauphinoise does not need cheese, herbs or nutmeg. The combination of garlic, salt and cream is sufficient, particularly if you're going to serve the gratin with something meaty and delectable (beef or duck would be excellent if you're having a blow out). Talking of accompaniments though, I happen to think that a slice of dauphinoise with just a sharply-dressed green salad (perhaps of young spinach or butter lettuce) on the side is a pretty perfect plate of food.
The instruction to simmer the potatoes in the cream and milk prior to baking is not, to my mind, necessary either. This method also means that the finished article is not attractively layered, but a bit more of a hotch-potch. Provided you bake the potatoes for long enough you will never end up with undercooked spuds, which seems to be the principal reason for advocating the technique.
To serve four:
5 large-ish Desiree potatoes
300ml of double cream
250ml of whole milk
Three cloves of garlic, minced
Small piece of butter
Salt and pepper
Pre-heat the oven to 190 degrees.
Thinly slice the potatoes (about 4mm thick). Mix the cream, milk and garlic together. Season very well with salt - when you taste the mixture it should seem oversalted, but don't worry as the potatoes will drink this up and the result will be perfect. Layer the potatoes in a baking dish measuring about 10" by 10", ensuring that you retain whole slices for the top layer. Over each layer pour a little of the mixture, and pour the rest over when you reach the top. Dot with butter and cover the dish with foil. Bake for an hour in the middle of the oven. After an hour, remove the foil and bake for a further 30 minutes after which the top should be golden and bubbling, and the potatoes soft and yielding when poked with a knife. If they still feel a little hard, put them back in the oven for a further 15 minutes or so.