My mom cut out this article from The Oregonian (article by Linda Faus and Danielle Centoni, notes in parenthesis by me) some years back. It is a very helpful article for insuring good, delicious cookies.
Too many recipes simply instruct bakers to “cream butter and sugar.” What that means is to beat them together at high speed until light and fluffy, usually for two to three minutes. The butter should be at room temperature unless specified otherwise. (I usually leave the butter out the night before I want to bake cookies–getting the butter to room temperature takes at least two hours, so plan ahead.) Cold butter straight from the fridge won’t cream properly.
Unsalted butter is generally recommended because some salted butters have more sodium than others. You can always add salt to a recipe but you can’t take it away.
As for the dry ingredients, test the potency of your stock of baking soda and baking powder before you begin baking: Baking soda should bubble when added to vinegar; baking powder should bubble when added to hot water. Be sure to mix them into the flour before adding to the wet ingredients; this distributes everything evenly so your cookies won’t end up with large holes.
Also, don’t be afraid to use the full amount of salt called for in a recipe, especially if you used unsalted butter. It might seem strange to add salt to a cookie, but the salt brings out and balances the sweetness; unsalted baked goods generally taste flat.
When it’s time to add the dry ingredients to the wet, mix just until blended; beating too long will only toughen the dough. Stir in anything chunky by hand, like chocolate chips and nuts, so your mixer doesn’t break them apart.
Some doughs work best when chilled before baking. (In fact, I chill all of my dough at least five minutes in the fridge. This allows the butter to solidify just a bit before baking. Otherwise, the butter tends to sink towards the bottom of the bowl and you end up with really buttery cookies by the last batch.)
Now it’s time to bake. Make sure the oven is fully preheated, and line your pans with parchment or silicone baking mats even if the recipe specifies an ungreased baking sheet. (I usually just spray the cookie sheets with cooking spray.) Invest in heavy pans, or double up your thin, flimsy ones to keep the cookies from burning on the bottom. Dark pans, too, tend to over-brown cookies.
Use a small ice cream scoop for effortless portioning and a picture-perfect, uniform size. (If you don’t have a small scoop, you can use two spoons.)
Bake a small batch first–say, four or five cookies–to make sure you’ve got the timing right. Everyone’s oven is different, and cookies may take more or less time in your oven than the recipe suggests. Some cookies are ruined when overbaked by just one minute.
Let the cookies rest on the baking sheet for a couple of minutes before transferring to a wire rack to cool. This will give them a little time to firm up so they don’t fall apart when moved.
Any baked cookie not frosted or glazed will freeze wonderfully in a self-sealing freezer bag. Or freeze scoops of dough on a baking sheet until hard, then transfer to a bag and freeze for up to several months. The frozen scoops can be placed on a baking sheet frozen; let stand for a few minutes to defrost and then bake as directed.
Cookies rolled in powdered sugar, like Russian Cookies, or Mexican Wedding Cakes, should be rolled twice to achieve that pretty, snowy look: Roll them first while they’re still a bit warm so the sugar adheres (it will melt a bit), then again when completely cool.