Preheat your oven to 375°F (190°C) and lightly grease a 9x13 inch baking dish.

Bring a large pot of salted water to a boil. Add the ziti and cook for 2 minutes less than the package directions (it should be very al dente, as it will continue cooking in the oven). Drain and set aside.

In a large skillet over medium-high heat, cook the ground beef, Italian sausage, and diced onion until the meat is browned and the onions are soft. Drain any excess fat. Add the minced garlic and Italian seasoning, cooking for 1 more minute until fragrant.

Pour the marinara sauce into the meat mixture. Stir well, reduce the heat to low, and let it simmer while you prepare the cheese layer.

In a medium bowl, combine the ricotta cheese, beaten egg, sour cream, parmesan cheese, chopped fresh basil, and 1 cup of the mozzarella cheese. Mix until smooth.

Spread about 1 cup of the meat sauce into the bottom of the prepared 9x13 dish. Add half of the cooked ziti pasta on top.

Spread the entire ricotta cheese mixture evenly over the pasta layer.

Add the remaining half of the ziti pasta on top of the ricotta layer. Pour the remaining meat sauce evenly over the pasta, making sure all the noodles are covered so they do not dry out.

Sprinkle the remaining 2 cups of mozzarella cheese evenly over the top.

Bake uncovered for 25-30 minutes, or until the edges are bubbling vigorously and the cheese on top is melted and starting to turn golden brown.

Let the casserole rest for 10-15 minutes before serving so the layers can set. Garnish with extra fresh basil if desired.