As I was planning my Xmas DInner (Asparagus Soup, Prime Rib, Carrots Julia (Child), Pommes Gratin Dauphinoise (more Julia), String beans, and Apple Crisp), I realized that one of my guests couldn't each much dairy and the Potato dish I was planning was loaded with butter, milk, and cream.
I vaguely remembered that there was an olive-oile based version, but not how it worked, so I decided to create something out of my taste memories rather than go hunting in my 5,000 cookbooks (I haven't even read the six new ones I got for Xmas).
I'm sure I'm reinventing something that already exists, but this is what I made:
Pommes Gratin avec Boef
(So named because I used beef stock as the liquid -- you could use chicken stock, too). Cut up potatoes and sice thinly, then cook until barely tender in stock with a bit of salt, pepper, and thyme. In the meantime, saute a chopped onion and some minced garic in a tablespoon of olive oil (amounts depends on how much you want, from one large potato and half an onion for one to vast multiples -- I'm usually making a dish like this for 6-8 and leftrovers are definited welcome.
When the onion is lightly browned, put the drained potatoes into a shallow baking dish, sprinkle with the onions and their olive oil, and add some of the cooking liquid (enough to come half way up the potatoes) and some salt and pepper. If you like, you can drizzle on a bit more olive oil or a few bits of butter. Bake in a 350 oven for about 1 hour until the liquid is mainly absorbed and the top is browned. My non-dairy eating friend loved her personal version of the potatoes and ate the leftover as a snack! Next time I'm making this version for everyone.