An oven thermometer is a necessity to make sure your oven is heating correctly. Many home ovens are off by 15 degrees, some by even 25 degrees or more! It may not seem like a big difference but baking at the wrong temperature can significantly change your final product.
Oven Rack Placement:
The position of your oven rack can also have a surprising impact on your cookies. Some recipes will specifically tell you where to position your oven rack, but most of the time it should be in the middle. Why? This is where the heat will concentrate and be most even.
If you bake your cookies (or anything else) on the top rack, there won’t be as much browning. On the bottom rack, there will be too much browning.
The same effect can occur when you’re baking multiple dishes at once. The other baking pans can block the heat from moving around freely and screw up the way the product is baked and browned. If you can, try to bake off one batch of anything at a time instead of doing multiple pans at a time.
Convention vs. Convection:
Unlike a convention oven, which is standard here in the U.S., a convection oven has a fan inside and an exhaust system that helps to circulate the hot air. This allows the oven to heat quickly and evenly, and to bake quickly and evenly. It’s more energy efficient and can even lead to better browning since the blowing air creates a drier environment. It bakes so much more evenly that you don’t actually need to rotate your baking trays.
Convection is great for savory preparations like roasts or anything that is covered like braising or casseroles. It’s good for cookies, pies, and pastries. It’s NOT good for delicate foods like custards, soufflés, cakes, and quick breads.
Convection Oven Temperature Reduction:
If you’re using a convection oven in place of a convention oven in a recipe, be sure to drop the temperature approximately 25°F. Also begin to check for doneness earlier, at least 2/3 to 3/4 of the way through the recommended baking time.