Awesome Baked Ziti

My neighbor brought this over when I had my baby. It has become a family favorite!

Awesome Baked Ziti
1 lb. dry ziti pasta
1 onion, chopped
1 lb. lean ground beef
2 (26 oz) jars spaghetti sauce
6 oz. Provolone cheese, sliced
1 1/2 cup sour cream
6 oz. Mozzarella cheese, shredded
2 TB grated Parmesan cheese

Cook pasta until al dente, about 8 minutes; drain. In a large skillet, brown onion and ground beef over medium heat. Add spaghetti sauce and simmer 15 minutes. Preheat oven to 350 degrees. Butter a 9X13 dish. Layer as follows: 1/2 of the ziti, Provolone cheese, sour cream, 1/2 sauce mixture, remaining ziti, Mozzarella cheese, and remaining sauce mixture. Top with Parmesan and bake for 30 minutes.