Bring a large pot of lightly salted water
to a boil.
Add ziti pasta, and cook until al dente, about 8
In a large skillet, brown onion and ground beef
over medium heat.
Add spaghetti sauce, and simmer 15 minutes.
Layer as follows:
½ of the ziti, Provolone
cheese, sour cream,
½ 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.