Bring a large pot of lightly salted water to a boil. Add pasta and cook for 8 to 10 minutes or until al dente; drain.
In a large skillet, brown beef over medium heat. Add onions; saute until tender. Drain off fat and add spaghetti sauce; 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.
