POLLO EN PIPIAN VERDE

Steps:

• Rinse chicken and cut garlic head in half crosswise. In a 6-quart kettle cover chicken, garlic halves, onion, coriander, salt, peppercorns, and allspice with water and simmer, covered, 1 hour, or until chicken is tender. Transfer chicken to a bowl to cool and reserve stock.
• Shred chicken, discarding skin and bones. Pour reserved stock through a fine sieve into a bowl, pressing garlic pulp through sieve. Measure 3 cups stock for sauce and reserve remainder for another use. Chicken and stock may be made 1 day ahead and cooled completely, uncovered, before being chilled separately, covered. (Stock keeps, frozen, 1 month.)
• Make sauce:
• Heat a large heavy skillet over moderate heat until hot and toast pumpkin seeds, stirring constantly, until they have expanded and begin to pop, 3 to 5 minutes. Transfer seeds to a plate to cool. In skillet heat sesame and cumin seeds, allspice, cloves, and peppercorns, stirring, until fragrant, about 1 minute, and transfer to plate. When seeds and spices are cool, in an electric spice/coffee grinder grind mixture in 4 batches to a powder.
• If using fresh tomatillos, discard husks and rinse with warm water to remove stickiness. Stem serrano chilies. In a saucepan simmer fresh tomatillos and serranos in salted water to cover 10 minutes. If using canned tomatillos, drain them and leave serranos uncooked. Transfer tomatillos and serranos (use a slotted spoon if simmered) to a blender and purée with onion, garlic, 1/4 cup coriander, and salt until completely smooth.
• In a 5-quart heavy kettle simmer tomatillo purée in lard or oil, stirring frequently, 10 minutes. Add 2 1/2 cups stock and stir in powdered pumpkin-seed mixture. Simmer sauce, stirring occasionally, 15 minutes, or until slightly thickened. Sauce may be prepared up to this point 1 day ahead and cooled completely, uncovered, before being chilled, covered.
• Roast and peel poblano chili . In blender purée poblano with remaining 1/2 cup stock and remaining 1/4 cup coriander until completely smooth. Stir poblano purée and chicken into sauce and heat on top of stove or in a 350° F. oven until chicken is heated through.
• Garnish chicken with pumpkin seeds and coriander and serve with tortillas.