THE WORDS au gratin in the name of a particular dish have come to indicate, in America at least, the presence of a topping of cheese. But in fact cheese has nothing to do with it, historically speaking. Gratin is a French word meaning the crust that forms on the bottom and sides of a dish of food that has been subjected to high heat.

Somewhere along the way this meaning literally got turned upside down and began to indicate the crust that forms on top of such a dish. Then, because the topping that most often helped a crust to form is cheese, the meaning got twisted into its present state.

Potatoes au gratin -- sliced potatoes baked in the oven with stock, milk or cream -- is the classic example of this type of dish, but even a tuna and noodle casserole can qualify as a grati'need dish if it has a crusty top. Creme bru le'e, that diabolically rich concoction involving lots of cream and a caramelized sugar topping, is a sweet example, as is apple crisp. The one characteristic that all these dishes have in common is that it's the crusty top that everybody at the table fights over.

The main idea, then, is to produce as much crust on top of the dish as possible. To do this, you need a very shallow, very wide pan so that the greatest possible amount of surface area can come in contact with the heat. The most wonderful pans for this enterprise are the sturdy, beautiful enameled cast-iron dishes made by LeCreuset and others. They invariably have cream-colored interiors and darker exteriors. They are designed to be both tough enough and good-looking enough to go from range to table. They can take the highest heat you can give them.

But because of their shape and configuration, and the material they're made of, they are useful for more than just making grati'need dishes. For one thing, they are fine for use on top of the stove as a saute' pan and in the oven as roasting pan. In a cast-iron gratin dish you can first sear the roast quickly on top of the stove, then put the whole thing in the oven to finish roasting. Their oval shape is perfect for rolled, tied roasts, for fish, even for chickens. And after the roast is finished you can deglaze the pan and make the sauce in it, too. They do not react with acid foods and they need no seasoning. And even if you cook the food somewhere else and assemble it for serving in the gratin dish -- paella might be an example of this -- the dish is ideal for reheating and serving.

Caring for these pans is no problem, even if, as is likely to happen when working with high heat, you overdo it at some point and let things burn. Generally an overnight soaking takes care of food that has burned itself to the sides, and a plastic scrubber gets off the stubborn bits. The LeCreuset people recommend against using abrasive cleansers and metal scrubbing pads, as these can make inroads on the enameled surface. They do recommend a bleach-water solution to get rid of any discoloration on the interior surfaces, although it's questionable whether a little discoloration isn't preferable to the risk of picking up a certain nuance of Clorox along with the tuna and noodles. Discoloration doesn't hurt anything.

The only real problem with enameled cast iron is a tendency to chip around the edges and then rust in the chipped places as the iron is exposed to air and water. This is purely a cosmetic problem and has no effect on the food that's being cooked.

In this country LeCreuset is sold in sizes measured in inches, but the number stamped into the bottom of each piece indicates size in centimeters. A "24," for instance, sold as an 11-inch dish, has a capacity of about 4 cups, meaning a gratin of potatoes made in it will serve about three people after allowing for shrinkage.

LeCrueset, and other enameled cast iron, is expensive, but there is no reason to pay full price. Kitchen Bazaar always has LeCreuset on sale, sometimes at 25 percent off list price, sometimes 35 percent, sometimes even 50 percent for discontinued colors. List prices range from $20 to $45.

Finally, for producing really crusty top crusts when your broiler is unequal to the task, there is an implement called a salamander. It's a heavy steel disk on a long handle. You heat the disk over a burner, then pass it across the top of the dish. Its classical use is with creme bru le'e, but it can be used for any dish whose top needs to be melted, browned or crisped.