Baked Ziti

1 lb dry ziti pasta (tube-shaped pasta; penne would also work)
1 onion, chopped
1 lb ground beef
2 jars spaghetti sauce
6 oz provolone cheese, sliced
1 1/2 cups sour cream
6 oz mozzarella cheese, shredded
2 Tbs grated Parmesan cheese

Boil ziti until al dente (about 8 minutes)
In large skillet, brown onion and ground beef.  Drain grease then add spaghetti sauce and simmer 15 minutes.
Preheat oven to 350 degrees
layer 9x13 pan or 2 8x8 pans like this (listed bottom to top):
1/2 of ziti
provolone
sour cream
1/2 of sauce
remaining ziti
mozzarella
remaining sauce
parmesan cheese

cover and bake for 30 minutes

NOTE: this freezes really well.  The sour cream and provolone are not classic Italian ingredients but they make it super creamy and gooey which I love:)