I think I may have written a post like this before, but some things are definitely worth repeating.
We've all done it. We've found the perfect cookie recipe, made a trip to the market for special ingredients, followed the instructions to the letter, popped them into the oven and out comes... Ugly cookies. Some burnt, some undercooked. All different sizes. Why is it that we can't all produce perfect, evenly baked, perfectly round cookies just like the pros do?
After years of cookie baking, I've learned a few things that help and I'd like to share them with you:
Invest in Good Pans
The secret to a good cookie starts with a standard aluminum "Commercial Half Sheet Pan". Not only are they sturdy, but they're NOT non-stick coated, which means they're light in color. Dark pans attract heat and will burn your cookie bottoms much easier than light pans. An added benefit is that you can scrub them clean with any abrasive cleaner without damaging them and they'll come squeaky clean. You can get one of these pans for $10-15 and they're worth every penny.
Forget the nonstick coatings (see above) and sprays and those reusable silicone mats. The only thing you need is parchment paper and there are two good reasons to spend the money on it. First, it's non-stick (duh). Second, the parchment provides just enough of an insulation barrier between the metal of the tray and your cookie's bottom to prevent over-browning. Let the cookies rest a few minutes on the tray after removing from the oven to "set" and then remove them to a cooling rack. Trust me when I say that parchment paper is the best $3.49 insurance you'll ever buy.
Want to know how bakeries get all their cookies to be the same size and shape? They use "dishers" (sweep-style ice cream scoops) to measure the dough. Choose one sized for the amount of dough the recipe calls for. You can try all you want to scoop by eye or use standard tablespoons but you'll rarely get consistent results.
Chill to Prevent Spreading
One of the more common problems with drop batter cookies is over-spreading, where your cookie bleeds out onto the plan flat as a pancake (and sometimes joins the cookie next to it). Most cookie recipes are based on shortening or butter and both are highly sensitive to heat. If you start with cold shortening, your cookie will spread less before it sets-up. Since the fat has to be room-temperature for mixing, you should chill your dough before baking. I even scoop dough onto trays, freeze it, then toss the balls of dough into zip-top bags. When I want cookies or unexpected guests arrive, I pull out a few balls, toss them onto a parchment-lined sheet, and bake about a minute more than the recipe called for.
Use Good Chocolate
If you're going to waste calories on treats, you might as well make sure they taste fantastic. Spending the extra dollar or so on quality chocolate chips is a great way to do that. I personally use nothing but Ghiradelli 60% Cacao Bittersweet Baking Chips. It's a great quality chocolate that's not the least bit waxy when baked and the 60% cocoa content pushes it just over into the realm of "dark chocolate" enough that it tastes incredibly rich but not bitter.