Preheat oven to 350 degrees. Spray a 9X13 inch baking dish with nonstick cooking spray.
Cook the spaghetti in well-salted water according to package instructions, just to al dente and drain well. Wipe out the pasta pot with paper towels and pour the well-drained pasta bake in the pot.
Add the beef, salt, and pepper to a large skillet and brown, breaking it up into medium chunks until there is no longer any pink. Drain excess fat. Pour beef into the pasta pot.
In the same skillet, brown the sausage, breaking it up into medium chunks, until cooked through. Pour the sausage into the pasta pot. Remove and discard all but 2 tablespoons of fat in the skillet. If there are not 2 tablespoons of fat, add vegetable oil.
Add the onion, garlic, and Italian seasoning to the skillet and saute on medium-low until onions are translucent. Pour into the pasta pot.
Pour the tomato basil sauce, sour cream, 1 cup mozzarella, and parmesan into the pasta pot and fold until everything is evenly combined and all the pasta is well coated in sauce.
Pour the pasta into the prepared baking dish and sprinkle the top evenly with the remaining mozzarella. Bake in preheated oven until bubbly, about 25-30 minutes. Sprinkle top with parsley and serve.