Baked Ziti

1. 1 pound dry ziti pasta
2. 1 onion, chopped
3. 1 pound lean ground beef
4. 2 (26 ounce) jars spaghetti sauce
5. 6 ounces provolone cheese, sliced
6. 1 1/2 cups sour cream
7. 6 ounces mozzarella cheese, shredded
8. 2 tablespoons grated Parmesan cheese

Bring a large pot of lightly salted water to a boil. Add ziti pasta, and cook 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 the oven to 350 degrees F (175 degrees C). Butter a 9×13 inch baking 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 grated Parmesan cheese. Bake for 30 minutes in the preheated oven, or until cheeses are melted.