If you do not have a baking sheet, a rimmed Pyrex dish, cast-iron skillet, or a makeshift tray folded from aluminum foil can serve much the same purpose. The important thing is to choose a rimmed, heatproof surface that fits inside the oven.
What Does a Baking Sheet Do?
A baking sheet distributes heat evenly, and its rim keeps liquid and fat from dripping onto the oven floor. The rim is especially useful for saucy dishes and greasy pastries. The material also affects the result: dark metal pans absorb heat faster and speed cooking, while light-colored pans cook more slowly and evenly. When you switch pans, watch the food and adjust the cooking time as needed.
What Can You Use Instead of a Baking Sheet?
A rimmed Pyrex dish comes closest for liquid-heavy or saucy dishes. Because glass retains heat differently, cooking may take a few minutes longer. A cast-iron skillet gives better browning underneath when a recipe calls for frying or charring, but its smaller size may mean you need more than one for a large batch. If you have no tray, you can fold the edges of a thick sheet of aluminum foil upward and lay it on the oven rack as a temporary tray. Use this only for short-cooking recipes with little liquid: during a long bake with plenty of liquid, the foil may tear and let liquid run onto the oven floor.
What Should You Watch Out For?
Do not put a cold glass dish straight into a hot oven; a sudden temperature change can crack the glass. Let the dish come to room temperature first. A cast-iron skillet can be heavy enough to strain an oven rack, so use the lower rack instead of the middle one to keep it balanced. For a tray-free bake, lowering the oven temperature by a few degrees and checking the food as it cooks can help you get close to the intended result.
What Should You Consider When Switching Between Dishes?
Different dishes retain heat for different lengths of time, so adjust the resting time after baking. A glass dish holds heat for longer and food may keep cooking after it leaves the oven; taking it out a few minutes early can help. A cast-iron skillet cools more quickly, so transfer the food to a plate right away if you want to serve it hot. If you put more than one dish in the oven at a time, leave enough space between them. Crowding reduces airflow and can lead to uneven cooking.
Choose an alternative dish that fits the oven. A dish placed too close to the door or heating element may cook unevenly, so choose one that can sit near the center. The recipe's basic principle stays the same: adjust the heat and cooking time to suit the dish for a result as close as possible to one made on a baking sheet.