Ancho chiles: When fresh poblano chiles are dried, they're called anchos. Mildly spicy, like the fresh counterpart, anchos develop a rich sweetness that is perfect for marinades or a simmering pot of chili.
Cilantro: This definitively Mexican herb is used only when fresh; it loses all flavor when dried. It provides an explosive sprinkle over lots of street foods, mostly as a component of salsa and guacamole. Store it wrapped in barely damp paper towels in a plastic bag in the warmest part of the refrigerator.
Dried guajillo chile: These smooth-skinned, brick-or cranberry-red chiles are a little spicier than anchos, and not nearly as sweet. They have a tangy brightness that leads many cooks to powder them over fresh fruit and vegetables, or to pair them with anchos in stews and soups.
Jicama: This long-lasting root vegetable is the color of a potato, and not much bigger. Peel, then eat raw for a slightly sweet, juicy crunch--perfect in slaws and chicken salad. Or eat it as Mexicans do, simply as a snack.
Masa harina: Corn tortillas are made from dried grain
(field) corn cooked with mineral lime then ground into a paste
called "masa." Several decades ago, a method was discovered to
dehydrate and powder the perishable masa; the result became known
as masa harina, or masa flour.
Poblano chiles: These mildly spicy, dark green fresh chiles are the size of a small bell pepper, but with a tapered point. The skin is tougher than a bell pepper, with more compact flesh, and more concentrated and complex flavor.
Queso anejo: This hard, aged cheese, made from cow's milk, adds a salty tang to whatever it touches. Dishes that always get a dusting of grated queso anejo, such as enchiladas, grilled corn on the cob, and street snacks made from corn masa, would be naked without it, like pasta without Romano or Parmesan.
Serrano chiles: These bullet-shaped, hot, green chiles are about 2 1/2 inches long and 1/2 inch wide. They have a punchy flavor that is heaven to green chile lovers--much less sweet than a jalapeno.