Baked Ziti

16 oz. dry ziti pasta (I actually used penne)
1 cup chopped onion (I use frozen)
2 lbs. lean ground beef
2 (26 ounce) jars spaghetti sauce
8 oz. provolone cheese, sliced
2 cups low-fat sour cream
8 oz. mozzarella cheese, shredded
2 T. Parmesan cheese

DIRECTIONS
1. Cook pasta according to package directions.
2. In a large skillet brown onion and beef. Add spaghetti sauce and simmer 15 minutes.
3. Preheat the oven to 350. Grease two 9x9 pans. 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 cheese.
4. Bake one pan for 30 minutes or until cheeses are melted. Cover and freeze other pan for another meal. I might even try splitting this recipe into four pans (or only making half the recipe) next time so that we don't have as many left-overs at one time.