For Tomatillo Salsa:
1/2 lb fresh tomatillos, husks discarded and tomatillos rinsed and quartered
3 fresh green serrano chiles, coarsely chopped (including seeds) 1/4 cup chopped white onion
3 garlic cloves, quartered
3/4 teaspoon salt, or to taste
1/2 cup water
2 tablespoons vegetable oil
3 tablespoons finely chopped fresh cilantro
1 to 2 tablespoons vegetable oil
12 (4-inch) corn tortillas
1 cup shredded cooked chicken (from 1 chicken breast half)
2 to 3 tablespoons crema or creme fraiche
1/3 cup finely chopped white onion
1/3 cup finely crumbled queso fresco (Mexican fresh cheese)
Puree tomatillos, chiles, onion, garlic, salt, and water in a blender until smooth.
Heat oil in a 10-inch heavy skillet over moderate heat until hot but not smoking, then carefully add tomatillo puree (oil will splatter) and simmer, stirring, until thickened, 8 to 10 minutes. Stir in cilantro and simmer 1 minute. Transfer to a small bowl.
Put oven rack in middle position and preheat oven to 200F.
Heat 1 tablespoon oil in cleaned dried skillet over moderate heat until hot but not smoking, then briefly cook tortillas, 3 at a time, until softened and hot but still pale, about 10 seconds per side, adding more oil if necessary. Transfer tortillas with tongs to paper towels to drain briefly, then to a large shallow baking pan in oven to keep warm, arranging tortillas in one layer (overlapping slightly if necessary) and covering pan with foil.
Spread each warm tortilla with about 1 teaspoon salsa, then top sparingly with a few shreds of chicken. Thin crema with a little water and drizzle over chicken, and then sprinkle with onion and cheese. Serve immediately.
Makes 12 chalupas.