You say escalloped and I say scalloped. You say scalloped and I say they are au gratin. You say au gratin and I say they are gratin dauphinois. You say I'm argumentative, and you are probably right. Enough said.
I've used this recipe for many years and most people say they are the best scalloped potatoes they have had. I believe I got the recipe from Julia Child's "Way To Cook" book but have since incorporated it into my own favorite dishes.
There are several key things to know when making this dish. After peeling, use a food processor to quickly and thinly slice good quality white potatoes. The processor ensures speed and a very evenly sliced batch of potatoes. Place them in lightly salted water to keep them away from the air while you make the cream sauce. Use that same food processor, blade change required, to finely chop an onion that you will sprinkle between the layers later.
Now make a good quality white cream sauce by making a standard roux (butter and flour cooked together for a few minutes, with some salt and white pepper) and adding whole milk and cooking until you have a silky, somewhat thickened mixture. Simply take care to continue stirring while cooking to make sure the milk does not scortch.
Finally, assemble by placing a layer of rinsed potatoes on the bottom of the buttered baking dish, topping with an even layer of cream sauce, then sprinkle with the chopped onion and repeating until the dish is full, ending with only cream on top. Dot the top with butter and bake. While I've put the full recipe in my Recipe Binder on my Facebook profile, you can see that this is not a particularly difficult dish to prepare. Further you may make it up to a day ahead, covering it tightly with plastic wrap having ensured that all the potatoes are covered with the cream sauce and refrigerating. Then just remove from the refrigerator for about 2 hours prior to baking.
As the sauce is made and thickened in advance, you need not worry about if it will thicken properly in the oven. Neither will you need to worry with stirring it during baking. It will brown and come out lovely and delicious every time. If you prefer, sprinkle with a mixture of bread crumbs and grated cheese about 30 minutes before the potatoes are completed. If you have other recipes for scalloped potatoes that you love, please pass them along!