The Classic Raw-Potato Method

• Many older versions of scalloped potatoes call for uncooked, thinly sliced russet potatoes. They're layered into a baking dish with some form of milk or cream and flavoring ingredients such as salt, pepper and onions. This style of scalloped potatoes cooks at low temperature for an extended period, often well in excess of 2 hours, which softens the russets and uses their high starch content to thicken the sauce to a silky texture. Some recipes recommend that you lend a hand by sprinkling flour or instant mashed potato flakes over the layers of russets to provide more and faster thickening. Cooked-potato versions of the dish take that a step further.

Not Created Equal

• Most recipes that begin with cooked or par-cooked potatoes abandon russets in favor of other potatoes such as Yukon Gold. Russets are a starchy potato variety, and when they're cooked or partly cooked they tend to lose their shape and crumble. "Waxy" potato varieties, sometimes called boiling potatoes, contain different starches and hold their shape nicely when cooked. They're a better choice if you want to cook your potatoes ahead of time, and they won't break down as the casserole bakes.

Replacing the Starch

• Waxy potatoes don't help thicken your sauce as russets do, so you'll need to replace that thickening power. One common strategy is to sprinkle flour or cornstarch over the potatoes as you layer them in, then moisten each layer with part of the recipe's milk or cream. You can substitute instant mashed potato flakes or refined potato starch -- available in some supermarkets -- if you wish to keep the dish potato-centric. Alternatively, you might opt to prepare a white sauce in advance by thickening milk or cream with your choice of starch. Using already-cooked potatoes with a finished sauce makes a very fast dish, needing only to be heated and browned in a hot oven.

Going for the Gusto

• If it's a special occasion and you want an extra-rich version of the potatoes, you can opt for a sauce made entirely with seasoned heavy cream. Heavy whipping cream is the base for many classical sauces; it only has to be simmered long enough for roughly half of its moisture to evaporate. You can pour the cream over your precooked potatoes and let it reduce in the oven or simmer it first in a saucepan and then pour it over the potatoes for a quicker finished dish. Brown the surface under your broiler at the end, with or without a garnish of cheese to enrich it further.