Tex-Mex Beef, Bean and Tortilla Casserole with Chipotles and Corn

3 tablespoons olive oil
3 cups chopped yellow onion
3 red bell peppers, finely chopped
8 garlic cloves, finely chopped
3 pounds very lean ground beef
2 teaspoons salt
6 tablespoons medium-hot chili powder
1 1/2 teaspoons ground cumin
1 1/2 teaspoons dried oregano, crumbled
1/2 teaspoon freshly ground black pepper
One 14-ounce can beef broth
1 3/4 cups canned crushed tomatoes with added puree
1 cup lager beer
3 canned chipotle chiles in adobo sauce, finely chopped
1 tablespoon adobo sauce, from canned chipotle chiles
One 1-pound package frozen corn kernels, thawed
1 1/4 pounds shredded sharp Cheddar cheese
1 pound shredded Monterey Jack cheese
24 6-inch corn tortillas
One 29-ounce can refried beans
3/4 cup chopped white onion
6 cups (about) finely shredded romaine lettuce
2 cups sour cream, room temperature, whisked until smooth

Heat oil in heavy large deep saute pan over medium heat. Add yellow onion, bell peppers and garlic. Saute until tender, about 10 minutes. Add ground beef. Sprinkle with salt. Saute until meat is no longer pink, breaking up meat with back of spoon, about 10 minutes. Add chili powder, cumin, oregano and black pepper; saute 3 minutes. Add broth, tomatoes, beer, chipotle chiles and adobo sauce. Simmer uncovered until liquid reduces slightly, stirring occasionally, about 40 minutes. Add corn and simmer until mixture thickens slightly, about 10 minutes. Remove from heat. Cool to room temperature. Cover chili and refrigerate at least 1 day.

DO-AHEAD TIP: Chili can be made up to 2 days ahead. Keep refrigerated.

Position rack in upper third of oven and preheat to 375 degrees F. Combine both cheeses. Spread 2 tablespoons beans over one side of 6 tortillas. Arrange tortillas bean side up and overlapping slightly in 14x11x3-inch baking dish. Spoon 1/3 of chili evenly over tortillas. Sprinkle 2 cups cheese mixture, then 1/4 cup onion over. Repeat layering 2 times. Spread remaining 6 tortillas with remaining beans, then arrange tortillas bean side down in casserole. Sprinkle with remaining cheese mixture.

Bake until casserole is heated through and bubbling, about 50 minutes. Let stand on cooling rack for 5 minutes. Cut casserole into generous squares. Sprinkle with shredded lettuce and top with dollop of sour cream, and serve.