Preheat the Oven
If food goes into the oven before it actually reaches the target temperature, the cooking time becomes unreliable; even when most home ovens indicate that they have reached the displayed temperature, the actual temperature inside may differ by a few °C, so preheating for 10–15 minutes makes a difference.
Putting the baking sheet in before preheating is complete can cause the inside to firm up before the outside cooks or the center of a cake to sink, because the first few minutes determine how the batter rises.
Choosing a Rack
The oven’s middle rack provides the most even heat distribution and is the default position for most recipes. Use the lower rack when you want to crisp the bottom quickly (for pastries or a pizza crust), and the upper rack when you want to brown the surface quickly.
If you are baking on multiple sheets at once, place them symmetrically in the center of the oven to allow air to circulate; otherwise, one sheet may cook less than another.
Difference Between Convection and Conventional Settings
A convection oven distributes heat more quickly and evenly, so when baking a recipe written for a conventional oven in a convection oven, you need to lower the temperature by about 15–20°C / 27–36°F or shorten the cooking time.
The convection setting is suitable for baking on multiple racks at once; the conventional setting provides gentler, more predictable heat for items that need a delicate rise, such as cakes and soufflés.
Choosing Bakeware
Glass and ceramic dishes heat slowly but retain heat for a long time; a metal baking sheet conducts heat quickly and promotes faster browning. If you change the bakeware for the same recipe, you may need to adjust the time by a few minutes.
When cooking chicken or fish in the oven, keep the cutting board and hands used to prepare the raw food separate from the cooked food and other ingredients; do not serve the food from the oven without checking its internal temperature. The target is 74°C / 165°F for chicken and 63°C / 145°F for fish.
Avoid opening and closing the oven door frequently; the temperature inside drops by a few °C each time, disrupting the rise of items such as cakes and soufflés. Oven cooking takes patience: starting before the oven reaches the right temperature can affect the result as much as choosing the wrong rack.