A sheet pan, also known as a baking tray, cookie sheet, or baking sheet, is a large flat metal tray used for cooking items in the oven. It is typically made of dark aluminum, though some smaller versions may be made of silicone. These sheet pans are available in a number of different sizes for different uses; most are rectangular in shape, but there are also round sheet pans available for making pizzas. A sheet pan is often sold in a multi-pack with a few different sizes and shapes of pans, to make it easier to find the correct size when needed.
Traditionally, a sheet pan is most often used to make cookies, though it may also be used for roasting items that need to lay flat, such as peppers or eggplant, or even for baking snacks like French fries or onion rings in the oven. These are just a few of the possible foods that could be cooked on this type of pan; it can be used for most things that do not produce a lot of liquid that could potentially spill off the sides. It is always a good idea to grease the sheet pan first with butter or cooking spray, or to line it with wax paper or aluminum foil, because these trays are notoriously difficult to clean and can become ruined if food gets stuck on them.
There are other uses for a sheet pan as well. Some people will place them under a casserole dish in the oven, if it seems likely that the casserole will bubble over and potentially get stuck to the oven walls. The pan underneath the dish can prevent this from happening. A sheet pan may also be used for broiling items such as steak, though it is a good idea to place a type of open rack in between the pan and the steak to allow it to drain, the way most broiling pans are designed.
Most sheet pans are made up of a single layer of aluminum, but insulated pans are available that feature a double layer. These are often a good choice for softer cookies or more delicate foods. Sheet pans designed for pizza will sometimes feature a number of small holes in the bottom of the pan, to allow the pizza dough to brown and become crispy. Sheet pans are typically quite inexpensive, and should be replaced if the non-stick coating begins to flake off.