Prep and Cook Time: about 2 hours to assemble, 2 3/4 hours to bake. Notes: Look for frozen banana leaves in Asian markets, and dehydrated masa flour in well-stocked supermarkets and Latino grocery stores. Assemble casserole up to 1 day ahead.
3 to 4 thawed frozen banana leaves (15 by 24 in. each; optional)
About 3 tablespoons salad oil
8 cups dehydrated masa flour (corn tortilla flour)
2 1/2 tablespoons baking powder
About 1/2 teaspoon salt
7 1/2 cups fat-skimmed chicken broth
How to Make It
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.
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.
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).
Arrange chicken mixture evenly in pan and spread level.
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.
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.
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.
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.