Most people add cheese to scalloped potatoes as a matter of course, though purists will claim that real scalloped potatoes are baked in a white sauce. It should go without saying that I belong to the purist school. I make a blond roux with butter, add enough whole milk or a mixture of whole milk and heavy cream to make a somewhat thin sauce, which I season with salt and white pepper. I then parboil red (waxy) potatoes, peel and slice thinly, layer them in a glass or porcelain baking dish, spooning the sauce between the layers. This is baked in a medium-high oven (350 or so) until the potatoes are tender through and the top somewhat browned.