Potato gratins are creamy, rich, and comforting—in other words, perfect cold-weather fare. There are two schools of gratin methodology: roux-based cheese sauce layered with potatoes, and potatoes simply bathed in cream and gilded with cheese. In both cases the potatoes (russets or Yukon Golds) should be sliced as thinly as possible, preferably with a mandoline if you’ve got one. Gruyère is classic, but any cheese that melts well, or a combination, will work in a potato gratin.
monavano, who is of the cheese sauce school, shares a basic recipe for the sauce:
2 tablespoons butter
2 tablespoons flour
2 cups milk
2 cups shredded cheese
1 teaspoon dried thyme
1/4 teaspoon nutmeg
Salt and pepper
Preheat oven to 400°F. Melt butter and add flour. Cook for a minute. Add milk and whisk until smooth. Increase heat and allow to thicken. Lower heat to medium and add cheese, thyme, nutmeg, and salt and pepper to taste. Layer potatoes, then sauce, potatoes, sauce, etc. Bake covered for 30 minutes. Uncover and bake for 10 minutes more. If you wish, add more cheese at the end and place under broiler to brown.
purple goddess adds crispy bacon bits to the cheese sauce and, after uncovering her gratin, tops it with a combo of seasoned breadcrumbs and cheese, dotted with butter; chef chicklet layers her potatoes with onions and grated cheese and pours cheese sauce over all.
linguafood offers a straightforward recipe from the cream-and-cheese-only camp:
1 pound potatoes, very thinly sliced
Salt and pepper
Pinch nutmeg (optional)
1 cup light cream
Preheat oven to 350°F. Layer potatoes evenly in a buttered baking dish. Mix garlic, salt and pepper to taste, and nutmeg (if using) into cream and pour over potatoes. Top potatoes generously with cheese and dot with butter. Bake for 45 minutes, or until golden brown.
Board Link: Au Gratin Potatoes---Your Best, Please