Potato Gratin

Baking potatoes, boiling potatoes, new potatoes, and fingerling potatoes—there are many kinds of each to choose from, some yellow, some blue or red. The red-skinned potatoes oft en called boiling potatoes have dense, white, waxy flesh that holds its shape when boiled. They won’t do very well for baking and make terrible mashed potatoes, turning gluey when mashed. Baking potatoes usually have light brown skins with white flesh that is dry and fluff y when cooked. These are best for baking and for French fries. Kennebecs and russets are common varieties. The tastiest, most versatile potatoes are the yellow-fleshed varieties such as Yellow Finn, German Butterball, and Yukon Gold. The flesh of these potatoes has a texture between that of a baker and a boiler. They have enough waxy starch to hold together when boiled, but not so much that they can’t be mashed—and best of all they are full of flavor, much more so than any white-fleshed variety. New potatoes are those that are dug while the plants are still green in the fields and have thin shaggy skins. They are a real treat. Fingerlings are smaller potatoes shaped, as you might guess, like long thin fingers. Some delicious varieties to try are Russian Banana, German, and Ruby Crescent. Select potatoes that are firm and free of discolored spots. Don’t buy potatoes that have green on the skin. This is caused by exposure to light and may indicate the presence of solanine, which is toxic. The green may be peeled away, but it is better to avoid having to do so. Store potatoes in a bag or cupboard away from any light. New potatoes and fingerlings never need to be peeled; just wash them well before cooking. Other potatoes should be peeled, depending on the recipe and your wishes. Once peeled, potatoes should be kept submerged in water to keep them from turning brown. I like this best when the potatoes are sliced quite thin (a mandoline makes this easy): that way the potato slices are less likely to curl up and burn on the edges. Yukon Gold and other waxy, yellow-fleshed potatoes keep their texture in a gratin; floury potatoes like russets fall apart.