Heat the oven to 375°F and grease a 9-by-13-inch baking dish.

Boil the pasta in salted water for 2 minutes less than the package directs, then drain.

Brown the beef and onion, drain well and stir in taco seasoning, tomato sauce and salsa; simmer for 3 minutes.

Remove from the heat and fold in sour cream, pasta and 1 1/2 cups cheddar.

Transfer to the dish, add the remaining cheddar and bake for 22 to 25 minutes until bubbling.

Rest for 8 minutes before serving.