Bring a large pot of lightly salted water to a boil. Add pasta and cook for 8 to 10 minutes or until al dente, then drain.
In a large skillet, brown beef over medium heat. Add onions and saute until tender. Drain off fat and add spaghetti sauce, then simmer for about 15 minutes.
Preheat oven to 350 degrees F (175 degrees C).
In a lightly greased 2 quart baking dish, place about half of the pasta; top with a layer of provolone and mozzarella cheese slices. Spread on a layer of half the spaghetti sauce mixture and sour cream.
Cover with remaining pasta, cheese and sauce. Sprinkle a layer of Parmesan cheese and fresh basil.
Bake in preheated oven for about 30 minutes or until cheese and sauce are bubbly. Serve.
