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

DIRECTIONS
1. Bring a large pot of lightly salted water to a boil. Add ziti pasta, and cook until al dente, about 8 minutes; drain.
2. In a large skillet, brown onion and ground beef over medium heat. Add spaghetti sauce, and simmer 15 minutes.
3. Preheat the oven to 350. Grease a 9x13 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.
4. Bake for 30 minutes in the preheated oven, or until cheeses are melted.

We had this the other night and it is super yummy. I only made half a recipe and it filled a 9x9 pan to the top, and we had lots of leftovers. Very yummy and easy!