This is a true Lyonnaise gratin. And it is VERY rich. A small portion is very filling. I had never eaten one so delicious before. I adapted this recipe after enjoying a similar one in a bouchon in Lyon on my first trip there. I was surprised to find that gratins in France contain proportionately much less cheese (sometimes there is NONE!) than what we here in US think is necessary.
My smarty-pants trick to ensuring the best potato gratin ever is cutting the crust that forms on top and gently folding it into the potatoes at least twice during the first half hour of baking. —ChefJune
Rub the inside of an oval porcelain gratin dish (about 14 x 9 x 2 inches) with the garlic. Arrange the potatoes in an even layer in the dish.
Mix the milk, eggs and salt and pour over the potatoes. Sprinkle generously with pepper.
Bake: occasionally cutting the crust that forms on top and gently folding it into the potatoes, until the gratin is golden, about 55 minutes. (This step is very important.)
Remove the gratin dish from the oven, sprinkle with the grated cheese, then dab the gratin with crème fraîche. Return the dish to the oven and bake until the top is very crisp and golden, about 15 minutes.
Let rest for 10 minutes before serving with other festive dishes. We love this for Christmas dinner with Prime Rib or Roast Goose.