1. Rinse chicken and pat dry; trim off and discard excess fat. Cut thighs in half. In a large bowl, mix chicken, 4 cups chipotle sauce, olives, and corn.
2. Rinse banana leaves and pat dry. Line a 12- by 17-inch roasting pan with 2 or 3 banana leaves so they extend above entire pan rim by 2 to 3 inches (if leaves aren't large enough, or if they split, overlap smaller pieces). Or omit leaves and rub pan with 1 tablespoon oil.
3. In another large bowl, mix masa flour with baking powder and 1/2 teaspoon salt. Add broth and mix until evenly moistened. Spread a 1/4-inch-thick layer of masa dough over bottom and up sides of pan (using about 5 cups).
4. Arrange chicken mixture evenly in pan and spread level.
5. Drop remaining masa dough in small dollops evenly over chicken mixture; gently spread to cover filling, sealing masa at pan rim. Drizzle top with 3 tablespoons oil, and with your fingertips, spread to coat surface. Fold leaf edges over masa and cover top with another banana leaf. If making up to 1 day ahead, seal pan with foil and chill. Also cover and chill remaining chili sauce.
6. Bake, covered with foil, in a 350° oven for 2 hours (2 1/2 hours if chilled). Remove foil; leave banana leaf in place (if used). Continue baking until masa is firm when pressed and a thermometer inserted in center of casserole registers 180° to 185°, about 45 minutes longer. Let stand at least 20 minutes.
7. Heat remaining chili sauce in a microwave-safe bowl in a microwave oven at full power (100%) until steaming, about 3 minutes, or stir in a 2- to 3-quart pan over low heat until hot, about 5 minutes. Pour into a serving bowl.
8. Lift banana leaf off top of casserole. Cut into portions and lift out with a wide spatula or use a large spoon to scoop to bottom of casserole. Add sour cream, salt, and extra chili sauce to taste.
Note: Nutritional analysis is per serving.