A Few Quick Notes Before You Start
Tossing in a cup of whatever rogue ingredient strikes your fancy is an easy and fun way to experiment in the kitchen (and is a lot less stressful than, say, experimenting with soufflés). Whichever goody you're baking, fold the mix-ins into the batter last, just before spreading into the pan (brownies) or dropping by spoonfuls onto sheets (cookies). Also, it's easier to cut brownies that have chunky additions (like nuts or candies) into squares if you line the pan with foil before pouring in the batter; once they're baked, chill the entire pan before you lift out the brownies and slice them. As for cookies, if you can stand the wait, chill the dough for 24 hours before baking. The cookies will spread evenly when they bake, won't get thin around the edges and will be thicker and chewier all over.