Besciamella sauce: heat butter in a medium sauce pan until melted. Add flour and stir until smooth. cook over medium heat until light golden brown, about 6 to 7 minutes. Meanwhile, heat the milk in separate pan until just about to boil.
Add milk to butter mixture 1 cup at a time, whisking continuously until very smooth and bring to a boil. Cook 30 seconds and remove from heat. Season with nutmeg and 2 teaspoons salt and set aside.
Preheat the oven to 425° f. Bring 6 quarts of water to a boil in a large pot and add 2 tablespoons salt (optional). Cook Ziti for 30 seconds less than the package instructions.
Add Marinara Sauce, besciamella sauce, Mozzarella, and grated cheese to the Ziti and mix well. Divide ziti and sauce mixture among six individual gratin dishes.
Sprinkle with breadcrumbs. Bake for about 20 minutes, until bubbling and crusty on top. Serve immediately.