Preheat oven to 350 degrees. Cook spaghetti according to package directions until just tender; drain.

In a large bowl, stir together ricotta, sour cream, cream cheese, half-and-half, mozzarella, Italian seasoning, garlic, salt, pepper, and half of the Parmesan cheese. Add cooked spaghetti and toss until well coated.

Pour the spaghetti mixture into a greased 9 x 13 pan. Top spaghetti with remaining Parmesan cheese. Cover with aluminum foil and bake for 30 minutes.

While the pasta is baking, prepare the meat sauce. Heat the oil in a large skillet. Add the onion and sausage and saute until the meat is cooked through and the onion is translucent. Add spaghetti sauce, adjust for seasoning, and simmer until the pasta is ready.

Remove the pasta from the oven and let it rest for 5 minutes. Cut the pasta into squares and top each serving with the meat sauce. Garnish with additional Parmesan cheese and fresh basil, if desired.