In saucepot, prepare ziti macaroni as label directs for minimum cooking time and do not use salt in water. Drain ziti and return to saucepot.
Meanwhile, remove casings from Italian-sausage links. In 12-inch skillet over medium-high heat, cook sausage meat until well browned, stirring occasionally to break up sausage. With slotted spoon, remove sausage meat to bowl.
Preheat oven to 375°F.; In drippings remaining in skillet, over medium-high heat, cook carrots, celery, and onion, stirring occasionally, until vegetables are golden and almost tender.
In 2-cup measure or medium bowl, with fork, mix milk and flour until smooth; stir into vegetable mixture in skillet. Add crushed tomatoes, sugar, dried basil, and pepper; over high heat, heat to boiling. Reserve 1 cup shredded mozzarella for topping.
Into cooked ziti in saucepot, stir vegetable mixture, sausage, and remaining mozzarella cheese. Spoon mixture into deep 3-quart casserole; sprinkle with reserved mozzarella cheese.
Bake casserole, covered, 15 to 20 minutes until cheese melts and mixture is hot and bubbly. Garnish with celery leaves.
Serves 8.
