Ingredients

• 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 (see cooks' note, below)
• 1 cup shredded cooked chicken (from 1 chicken breast half)
• 2 to 3 tablespoons crema or crème fraîche
• 1/3 cup finely chopped white onion
• 1/3 cup finely crumbled queso fresco (Mexican fresh cheese)

Instructions

1. Purée tomatillos, chiles, onion, garlic, salt, and water in a blender until smooth.
2. Heat oil in a 10-inch heavy skillet over moderate heat until hot but not smoking, then carefully add tomatillo purée (oil will splatter) and simmer, stirring, until thickened, 8 to 10 minutes. Stir in cilantro and simmer 1 minute. Transfer to a small bowl.
3. Make chalupas: Put oven rack in middle position and preheat oven to 200°F. 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.
4. Put oven rack in middle position and preheat oven to 200°F.
5. 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.
6. 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, then sprinkle with onion and cheese. Serve immediately.