8 ounces (5-6 medium) tomatillos, husked and rinsed (see cook's notes)
2 fresh serrano chilies, or to taste, stemmed
1 1/2 tablespoons olive or vegetable oil, divided use
1/2 medium white onion, roughly chopped
1 garlic clove, peeled and roughly chopped
1 cup chicken broth
3 tablespoons roughly chopped cilantro
Salt, 1/4 to 1/2 teaspoon, depending on saltiness of broth
12 warm corn tortillas (plus a few extra, in case some break)
2 cups firmly packed sliced chard or spinach (all pieces should be about 1/2 inch wide and 2 inches long)
1 1/3 cups coarsely shredded cooked chicken
1/2 to 3/4 cup crumbled Mexican queso fresco
1. 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.
2. 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.
3. 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.
4. 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.
5. 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.
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.
