1. Preheat the oven to 375°F and grease a 9×13-inch baking dish.

2. Bring a large pot of salted water to a boil and cook the ziti until just under al dente. Drain and set aside.

3. Heat the olive oil in a large skillet over medium heat and cook the Italian sausage until browned and crumbled.

4. Add the diced onion and cook until softened, then stir in the garlic and cook for 30 seconds.

5. Pour in the marinara sauce and crushed tomatoes, then add the Italian seasoning, red pepper flakes, salt, and black pepper. Simmer for 5 to 7 minutes.

6. In a medium bowl, mix the ricotta cheese, egg, Parmesan cheese, and 1 cup of the mozzarella cheese until smooth.

7. Toss the cooked ziti with most of the sausage sauce, reserving a little sauce for the bottom of the baking dish.

8. Spread a thin layer of sauce in the prepared baking dish, then add half of the pasta mixture.

9. Spoon half of the ricotta mixture over the pasta and sprinkle with 1 cup of mozzarella cheese.

10. Repeat with the remaining pasta, ricotta mixture, and mozzarella cheese. Top with the last bit of sauce and remaining cheese.

11. Bake uncovered for 25 to 30 minutes, until hot and bubbly and the cheese is lightly golden.

12. Let the baked ziti rest for 10 minutes, then finish with fresh basil before serving.