This is really one of the simplest and yummiest potato dishes I have ever made.
When I was a nanny in France, Marie-Laure (my boss) taught me the tricks of the trade for Gratin Dauphinois.
I used to believe that Gratin Dauphinois was one of the most difficult dishes to make, but it really is soooo easy.

(Serves 4 people)
1kg potatoes
2.5 dl cream (I use half fat cream, but that's by choice)
0.5-1 dl white wine (this is optional but does give a good taste to the dish)
200g grated Gruyère cheese (if you can't get your hands on Gruyère, you can use any hard cheese)
1 clove garlic (crushed)
salt and pepper
Peel and thinly slice the potatoes.
Rub the bottom of the dish with some garlic and pour in enough cream to cover the bottom of the dish.
(so that the potatoes don't stick)
Put two layers of potatoes in the dish and sprinkle with garlic, salt, pepper and cheese.
Cover with cream and eventually a little white wine.
Continue the layers in order to fill the dish.
Add more cheese to the last layer so that the Gratin will have a cheesy crust.
Cook at 200°C for about an hour or until potatoes are cooked. Check by inserting a knife.
Take out of the oven and leave to stand for 5 minutes before serving.
Tip: When I've finished the layers, I tip the dish to check I have enough liquid for the cooking.
(not too little and not too much)

It really is up to you how much liquid you use.
Over the years, I've modified the measures for my personal taste.
The first few gratins were trial and error!
Bon Appetit