Bring a large pot of lightly salted water to a boil. Add ziti pasta, and cook according to package directions until al dente. Drain, rinse under cold water, and set aside.

Heat olive oil in a large skillet over medium-high heat. Add onions and garlic, and saute for 3 minutes. Add crushed tomatoes, Italian seasoning, salt and pepper to taste, and chopped basil leaves. Let the sauce simmer on low for about 20 minutes, stirring occasionally. Remove from heat and let cool (makes about 2 1/2 cups).

Preheat oven to 375 degrees. Lightly grease a 9X13-inch baking dish and set aside.

In a large bowl, mix together 1 cup of ricotta cheese, 1/2 cup of mozzarella cheese, 1/4 cup of Parmesan cheese along with an egg. Season with salt and pepper. Stir in about 1 1/2 cups of cooked tomato sauce. Pour the pasta into the bowl with the cheese mixture and toss to coat.

To assemble the casserole, add half of the coated pasta to a baking dish, then dot the surface with 1/2 cup of ricotta cheese. Add the rest of the pasta and sauce on top and press the pasta down gently so it doesn't stick above the sauce too much. Top with dollops of the remaining ricotta cheese and sprinkle on top with the remaining mozzarella and Parmesan cheese.

Bake uncovered for 20 minutes, or until lightly browned and bubbling around the edges. Remove from oven and let stand 5 minutes before serving. Sprinkle with additional fresh chopped basil, if desired, and serve.