The beauty of this grilled tamarind chicken is both its sharp and piquant flavor and its simplicity. A potent tamarind-and-chipotle marinade renders a richly flavored, juicy, and tender chicken in mere minutes, making it equally suited for a weeknight meal or a dinner party. The tamarind concentrate in the marinade adds a sour funk that complements the freshness of the cilantro leaves and smoky heat of the chipotle chile paste. The marinade gives the chicken a dark, lacquered appearance and will char a little as it cooks, becoming caramelized, chewy, and ultimately, mouthwateringly delicious. Grilling the chicken over coals will naturally impart a more smoky finish, while roasting the chicken in the oven (see Note) will produce the liveliest sour and spicy flavors.