A baking sheet is a flat metal pan characteristically used in either the oven or the broiler. It is only a single layer unless it is an insulated pan, which is made of two sheets of aluminum with a layer or air sealed between them. While an insulated baking sheet is a good choice for softer baked goods, a dark single sheet will help to crisp items. Single sheets can be stacked double to imitate the effect of an insulated pan, if desired. Typically, they are greased or lined with parchment prior to use, although some items may be placed directly on the metal surface.
Another popular use of a baking sheet is to toast or roast items that do not contain a lot of liquid that could run over the edge. Items that may be toasted include nuts, pumpkin seeds, and bread cubes oiled and seasoned to make croutons. Garlic bread can also be toasted this way. Roasting on a baking sheet works for squash, onions, peppers, and eggplant in the skin, and when carefully done, leaves the vegetables browned on the outside and tender inside.
Some quick breads are baked on a baking sheet. Scones — which may be shaped as triangles, rounds, squares, or diamonds — are prepared in this way. So are biscuits, including baking powder biscuits. Popovers and muffins, on the other hand, are baked in specially prepared tins.
Turnovers from a variety of cultures may be baked on a baking sheet. This includes empanadas, which are Mexican or Spanish pastries; calzones, which are Italian turnovers; the turnovers from Crete called Skaltsounia; and Indian samosas. Dessert turnovers are baked this way as well. Other items that may cooked on this pan include pretzels, crackers, crabcakes, and pizza.