Preheat oven to 400°.
Combine first 5 ingredients in a small bowl, and rub over chicken. Place chicken pieces in a 13 x 9-inch baking dish; add broth and the next 5 ingredients (broth through tomatoes). Cover and bake at 400° for 1 hour or until chicken is done. Serve the tagine over couscous, and garnish with cilantro sprigs, if desired.