Baking Cookies On The Top Rack Is A Grave Mistake
Many of us who bake cookies at home think it doesn't matter which rack we use in the oven. They all look the same other than their heights, so they should all cook the same, right?
Well, not quite. Seasoned bakers take oven rack placement seriously for a reason. In a typical electric oven, you'll have two heating elements that generate heat to cook your food — one at the top used for broiling, and one at the bottom for baking. As such, when you put your cookies in and turn the setting knob for "Baking," the heat will come mostly from the bottom of the oven.
This doesn't mean that the bottom racks are the hottest, though. It's actually the complete opposite: Warm air rises, so it's the top racks that will get the hottest. If you've ever tried baking a large batch of cookies and used up all the racks, you'll very likely find the ones at the top to be a bit browner or even burnt compared to the ones down below. In that case, you've fallen for the "top rack trap."
The middle rack is where it's at
Ovens are pretty fascinating when you look into them. More than just metal boxes with heaters built in, they're designed to circulate whatever heat they generate around the entire chamber as efficiently as possible. This doesn't mean they're able to do it perfectly, unfortunately. As mentioned earlier, hot air naturally rises, so the top rack consistently ends up being the hottest spot in the oven. While this is great for dishes like lasagna or casseroles that benefit from a browned top, it's not ideal for baking cookies. The bottom rack isn't as hot as the top, but it's still pretty warm. It's commonly used for pizzas, where a nicely cooked bottom is what you're after.
Now, the middle rack — that's what you'll want to use when you're baking cookies. The middle rack is the Goldilocks zone, where the heat is neither too hot nor too cold — just right. All your chocolate chip cookies baked on this rack will have the best chance of coming out golden brown, without any burnt tops or undercooked middles.
Out of space? Juggle the racks!
Of course, sometimes you need to bake more than one batch of cookies at the same time. If you find yourself with a double batch that needs to be baked on two racks, don't worry. The middle and the bottom rack are both open for use, though you'll have to get a little bit handy (literally, with a pair of oven mitts) for them to turn out just right.
Here's a tip that's well worth a try: Place two baking sheets in the lower and middle rack and add two extra minutes to the overall baking time. Start the timer, and when the cookies are halfway through their baking time, move the bottom tray up and the top tray down. This way, by the time the full baking time is finished, every cookie will have gotten a turn in the middle rack sweet spot, and you'll get a batch of cookies that are just right on every try.