Heat the oven to 350°F (175°C) and lightly grease a 9-by-13-inch baking dish.

Brown the lean ground beef in a skillet over medium-high heat, breaking it into small crumbles. Drain any excess fat, then stir in the taco seasoning and the amount of water listed on the packet, usually ¾ cup; simmer for 3–5 minutes until thickened.

Warm the refried beans briefly so they spread easily, and warm the tortillas just enough to make them flexible. Stir the condensed tomato soup and sour cream together in a bowl until creamy.

Layer tortillas, seasoned beef, refried beans, the soup mixture, and shredded cheddar in the baking dish. Repeat the layers as needed, finishing with a generous layer of cheese.

Cover the dish loosely with foil and bake for about 20 minutes. Remove the foil and continue baking for another 5–10 minutes, until the cheese is melted and bubbling.

Let the casserole rest for 5 minutes before slicing and serving. This short rest helps the creamy layers settle so each portion is easier to lift.