Baked Ziti

1 pound dry ziti pasta
1 onion, chopped
1 pound lean ground beef
2 (26 ounce) jars spaghetti sauce
6 ounces provolone cheese, sliced
1 1/2 cups sour cream
6 ounces mozzarella cheese, shredded
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.

Heat the oven to 350 degrees F (175 degrees C). Butter a 9 x 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 or until cheeses are melted.