Tomatillo Chicken Tacos

8 oz. (5-6 medium) tomatillos, husked and rinsed (see cook's notes)

2 fresh serrano chilies, or to taste, stemmed

1 1/2 T. olive or vegetable oil, divided use

1/2 medium white onion, roughly chopped

1 garlic clove, peeled and roughly chopped

1 C. chicken broth

3 T. roughly chopped cilantro

Salt, 1/4 to 1/2 t., depending on saltiness of broth

12 warm corn tortillas (plus a few extra, in case some break)

2 C. firmly packed sliced chard or spinach (all pieces should be about 1/2 inch wide and 2 inches long)

1 1/3 C. coarsely shredded cooked chicken

1/2 to 3/4 C. crumbled Mexican queso fresco

Roast tomatillos and chilies on baking sheet 4 inches below a very hot broiler until blackened and soft on one side, about 5-6 minutes, then turn over and roast on other side, 3-4 minutes. Transfer (including all juices) to a food processor fitted with the metal blade or to a blender.

Heat 1 tablespoon of oil in a large, heavy skillet over medium heat. Add onion and cook, stirring frequently, until deep golden, about 8 minutes. Stir in garlic, cook 1 minute, then scrape into food processor or blender. Process to medium-coarse puree.

Heat 1/2 tablespoon oil in skillet over medium-high heat. Add puree and stir for about 5 minutes, until noticeably darker and thick. Stir in broth, partially cover and simmer over medium-low heat for 10 minutes. The sauce will be a little soupy. Stir in cilantro and generously season with salt.

Bring sauce to a boil and add greens. When the mixture returns to a boil, stir in chicken and simmer until greens are done. Taste and season with additional salt, if needed.

Guests will spoon a portion of filling into warm tortilla, sprinkle on cheese and fold it over. As with all these tacos, fold and eat immediately.

Advance preparation: The Tomatillo-Serrano Sauce (the procedure through step 3) can be prepared several days in advance and stored in the refrigerator, covered. Reheat and finish as directed.

Source: adapted from "Mexican Kitchen: Capturing the Vibrant Flavors of World-Class Cuisine," by Rick Bayless with Deann Groen Bayless and Jean Marie Brownson

Yield: About 3 cups of filling, enough for about 12 tacos.

Cook's note: Tomatillos look like small green tomatoes covered with a thin, parchment-like covering. The flavor has hints of lemon, apple and herbs. Choose tomatillos with dry, tight-fitting husks.