Q. How do you keep scalloped potatoes from curdling?
Use heavy cream, of course! Fat reduces the tendency of milk and cream to curdle, so the higher the fat content, the less likely it is to curdle. Now, we hear you muttering "fat chance" about the likelihood of using heavy cream to make your scalloped potatoes with the emphasis on "fat." So we'll offer a couple other tricks to help keep your potatoes skinny and uncoagulated.
Although milk is a fairly stable substance, it curdles readily when it comes in contact with an acid or salt in the presence of heat e.g., a gratin pan of salted potatoes in your oven. We've already mentioned that fat blocks or postpones the curdling. Starch is another weapon in your arsenal. If you use starchy potatoes, such as russets, more of the potatoes' starch will leach into the milk, thickening it and inhibiting the inclination to curdle. You can also thoroughly blend a teaspoon of flour for each cup of milk used in your dish, and that alone will almost certainly prevent curdling, even if you use skim milk.
The fresher your milk, the less likely it is to curdle. Also the use of moderate heat (325°F to 350°F; 160°C to 175°C) may help, as much of the milk can be absorbed by the potatoes before it gets so hot that it curdles.
Here's a simple French recipe (with a fancy name) for scalloped potatoes that takes the middle ground and uses half-and-half instead of milk or cream:
From The Great Potato
Book (Canada, UK), by Florence Fabricant.
Among the simplest ways to glorify potatoes is to bake them in cream with garlic, a sinfully rich classic that originated in a mountainous region in eastern France. A potato with a high starch content, like the Russet, helps thicken the cream, and with russets you can also spare much of the fat by using milk instead. The gratin can be held, once it has finished baking, loosely covered in a warm oven for up to 30 minutes.
1 tablespoon unsalted butter
3 cups half-and-half
4 cloves garlic, smashed
3 pounds Russet potatoes, peeled and sliced 1/8 inch thick
Salt and freshly ground white pepper
Preheat the oven to 350°F (175°C). Butter a 6-cup gratin dish or baking dish 1-1/2 to 2 inches deep.
Place the half-and-half in a 3-quart saucepan. Add the garlic and potatoes and bring to a simmer. Season with salt and pepper. Simmer for 5 minutes, then transfer to the prepared gratin dish.
Place in the oven and bake for about 40 minutes, until the top is golden brown, the potatoes are tender, and much of the half-and-half has been absorbed. Serve hot.
Gratin Savoyard Variation:
Substitute well flavored beef or chicken stock for the cream and you have a lighter dish, a gratin Savoyard. It's especially good with a topping of shredded Gruyère cheese dotted with butter. Sautéed mushrooms can also be added to it, and crumbly goat cheese can be substituted for the Gruyère.
Yield: 6 Servings