Preheat oven to 375°F.

Melt butter in a large skillet over medium-high heat.

Add onion and next 3 ingredients; cook, stirring occasionally, 8 to 10 minutes or until softened and lightly browned.

Stir in garlic, chili powder, cumin, salt, and black pepper; cook, stirring occasionally, 1 minute.

Sprinkle flour over vegetable mixture, and cook, stirring constantly, 1 minute.

Whisk in broth, and increase heat to high. Bring to a boil, stirring constantly.

Boil, stirring occasionally, 1 to 2 minutes or until thickened. Remove from heat.

Stir in tomatoes and sour cream.

Stir together chicken and cilantro in a large bowl; stir in vegetable mixture.

Combine both cheeses in a small bowl.

Heat a large cast-iron skillet over high heat.

Lightly brush each tortilla on both sides with oil.

Cook tortillas, in batches, in hot skillet 1 to 2 minutes each side or until lightly browned and crisp on both sides.

Line bottom of a lightly greased (with cooking spray) 13- x 9-inch baking dish with 6 tortillas, overlapping slightly, to cover bottom of dish.

Top with half of chicken mixture and one-third of cheese. Repeat layers once.

Top with remaining tortillas and cheese.

Lightly coat a sheet of aluminum foil with cooking spray, and cover baking dish.

Bake at 375°F for 20 minutes.

Uncover and bake 10 minutes or until bubbly and lightly browned on top.

Let stand 10 minutes before serving.