01 -
Preheat the oven to 350°F (175°C). Lightly grease a 9 x 13-inch baking dish.
02 -
Heat olive oil in a large skillet over medium-high heat. Add the ground beef and onion, then cook for 6-8 minutes, breaking up the meat, until the beef is browned and the onion is soft. Drain excess fat.
03 -
Stir in taco seasoning, black beans, salsa, salt, and pepper. Simmer for 3-4 minutes, until the mixture thickens slightly. Taste and adjust the salt if needed.
04 -
In a bowl, whisk together sour cream, condensed cream of mushroom soup, and milk until smooth.
05 -
Spread a thin layer of sauce in the baking dish. Add overlapping tortillas, half of the beef filling, more sauce, and 1 cup of cheese. Repeat with another tortilla layer, the remaining beef, more sauce, and 1 cup of cheese. Finish with tortillas, the remaining sauce, and the last cup of cheese.
06 -
Bake uncovered for 25-30 minutes, until the cheese is melted, the edges bubble, and the top has golden spots.
07 -
Let the casserole rest for 10 minutes before slicing. Top with cilantro, tomatoes or jalapeños if using, and serve with lime wedges.