6 ounces dried fettuccine –preferably spinach
2 teaspoons canola oil
3 leeks — white parts only-washed and finely chopped-1 1/2 cups
6 ounces button mushrooms — quartered
1 teaspoon chopped fresh rosemary
3 tablespoons all-purpose flour
3 cups reduced-sodium chicken broth — defatted
1/2 cup 1% milk
2 cups cubed cooked chicken breast
fresh lemon juice — to taste
salt & freshly ground black pepper — to taste
1/3 cup freshly grated Parmesan cheese
1/4 cup fine dry breadcrumbs
grated zest of 1 lemon
1 tablespoon finely chopped fresh parsley
Preheat oven to 425ºF. Lightly oil a 3-quart baking dish or coat it with nonstick spray.
Cook fettuccine in boiling salted water until al dente, about 8 minutes. Drain and refresh under cold running water. Drain and set aside.
Meanwhile, in a large skillet, heat oil over medium heat. Add leeks and cook, stirring, until lightly browned, 6 to 8 minutes.
Add mushrooms and 1/2 teaspoon rosemary; cook, stirring, until softened, about 5 minutes. Add flour and cook, stirring, for 1 minute. Add chicken broth and milk; bring to a boil, stirring, until slightly thickened, about 4 minutes more. Remove from heat and stir in chicken. Season with lemon juice, salt and pepper.
Gently mix reserved fettuccine into chicken mixture and spoon into prepared baking dish.
In a small bowl, combine Parmesan, breadcrumbs, lemon zest, parsley and remaining 1/2 teaspoon rosemary. Season with salt and pepper. Sprinkle mixture over the casserole. (The casserole will keep, covered, in the refrigerator for up to 2 days.)
Bake casserole for 20 to 30 minutes, or until bubbling. Let stand for 5 minutes before serving.