Brown beef and onion; drain.
Add taco seasoning and stir in refried beans.
Mix soup and sour cream in a separate bowl.
Spread ½ sour cream mixture in the bottom of a casserole dish.
Tear up 3 tortillas and spread over sour cream mixture.
Put ½ the meat bean mixture over that.
Add a layer of cheese.
Repeat the layers.
Sprinkle cheese over the top and bake, uncovered, at 350°F for 20-30 minutes.