There are those weeknights when I'm happy to come home and whip up a relatively complicated dinner—something like a lasagna or an eggplant Parmesan—but on most nights, I want something as quick and straightforward as possible. That means quesadillas are in regular weeknight rotation at my house. And, since the quesadillas themselves are so simple to make (not to mention the perfect way to use up leftover beans or roasted meats), they free me up to invest in a crowning touch that improves them immeasurably: an easy salsa verde made with charred tomatillos, onions, and chilies.
Blistering the skins of the component ingredients may be an extra step, but it's a critical one for making a standout salsa, bringing out the sweetness in the vegetables and adding a rich, smoky flavor. You can do it by holding the vegetables with tongs directly over a gas flame, if you have one, or with a blowtorch. The easiest and least messy approach, though, is to place them on a foil-lined baking sheet and stick them under a preheated broiler. Once they're sufficiently blackened, just dump the vegetables and their exuded juices into a blender with a big handful of cilantro, process them to a rough purée, season with salt to taste, and your salsa verde is done.
But this method isn't applicable only to salsa: It works for any recipe in which a little charred flavor in your vegetables would be welcome. In Thailand, an open flame is often used to make the excellent-on-everything roasted-chili dip nam phrig noom, but using a broiler to char the shallots, chilies, and garlic will work just as well. And we've got a number of chili recipes in which the technique is essential to developing a more complex flavor base.
Remember that you're looking for a good, even char here to ensure maximum smoky effect—that'll make an appreciable difference in the resulting sauce—so keep an eye on your ingredients as they broil. As with anything, attention to the small details will pay off in the end.