Many time-conscious cooks prepare a double batch of vegetables, serving half steamed or sauteed one day and turning the rest into a gratin the next.
The crust that forms during baking gives this fancy casserole its name. Gratiner in French means "to bake until crusty." You can make gratins without sauces, too, simply by moistening the vegetables with a little butter or a flavorful oil to keep them from drying out and to make the topping adhere.
These simple, sauceless gratins are popular in Mediterranean homes. In A Spanish Family Cookbook (Interlink, 1997), Juan and Susan Serrano prepare a leek gratin with crisp bacon and tasty Spanish manchego cheese. Karyl Bannister, the author of Cook & Tell (Houghton Mifflin, $23), likes a fresh corn gratin with sauteed tomatoes crowned with tiny cubes of buttered bread.
The crust of a gratin can be delicate or crunchy. Grated Parmesan or Gruyere cheese, sometimes mixed with bread crumbs, is the traditional topping.
American cooks often choose sharp cheddar. I occasionally use assertive cheeses such as French Cantal, Italian Asiago, Greek kefalotyri or Eastern European kashkaval.
For a new twist, I sometimes opt for chopped nuts, which give a delicious crust that's crunchier than cheese or bread crumbs. I love pecans, walnuts and almonds, but any kind of nut will work. The nuts become toasted and their taste intensifies as they bake with the vegetables.
Once in a while, I even sprinkle my gratin with seeds, whether sesame, sunflower, or Mexican pumpkin seeds (pepitas).
A cheese sauce isn't your only option when making saucy gratins. A nutmeg-scented cream sauce is nice for delicate dishes, and tomato sauce is perfect for a more robust coating. You can also use prepared enchilada sauce or spaghetti sauce.
