- Cook ground beef and onion in a skillet until meat is browned, stirring to crumble meat.
- Drain. (I add onion after beef is cooked and drained to limit amount of fat absorbed by onion)
- Add taco seasoning mix and water, stirring well.
- Bring to a boil; reduce heat, and simmer 20 minutes, stirring occasionally.
- Combine refried beans and ⅓ cup taco sauce.
- Spoon half of bean mixture in bottom of pastry shell.
- Top with half of meat mixture, half of cheese and all of corn chips.
- Repeat layers with remaining bean mixture, meat mixture, and cheese.
- Bake at 400 °F for 20–30 minutes.
- Serve with shredded lettuce, chopped tomato, sour cream (if desired) and remaining taco sauce.