Creamy chicken-noodle casserole with spinach and mushrooms

Chicken breast, boneless, skinless	1 pound
Water	1 ½ cups
Garlic, minced	3 cloves
Bay leaf	1
Flour	1/3 cup
Cornstarch	2 tablespoons
Milk	2 cups
Tarragon, dried	1 teaspoon
Salt	1 teaspoon
Nutmeg, freshly ground	1/8 teaspoon
Wine, dry white	¼ cup
Spinach, frozen, thawed, squeezed dry	10 ounces
Linguine, spinach, cooked al dente	10 ounces
Mushrooms, quartered	1 pound
Salt
Pepper, freshly ground
Butter	1 tablespoon
Breadcrumbs, fresh French, coarsely chopped	1 cup
Parmesan cheese	½ cup + ½ cup
Asiago cheese, shredded	½ cup + ½ cup

1. Preheat oven to 400°F. 
2. Combine chicken, 1 cup water, garlic, and bay leaf in large saucepan. 
3. Cover and simmer until chicken is cooked, turning once, about 15 minutes. 
4. Transfer chicken to a plate to cool, and then shredded. 
5. Reserve the cooking liquid, and add water, if necessary, to measure 1 cup. 
6. Whisk flour and cornstarch together in a heavy, large saucepan. 
7. Add 1 cup milk, whisking until smooth. 
8. Over medium heat, stir in 1 cup milk, tarragon, salt, nutmeg, and reserved chicken cooking liquid. 
9. Stir until thick and boiling, about 5 minutes. 
10. Add wine, and stir until mixture is very thick, about 2 minutes longer. 
11. Remove from heat. 
12. Stir in shredded chicken and spinach, and then add noodles and mushrooms. 
13. Transfer to a 11x7x3-inch glass baking dish, and season with salt and pepper. 
14. In a medium skillet, melt butter over medium-high heat. 
15. Add breadcrumbs, and stir 1 minute. 
16. Sprinkle over casserole, and sprinkle with ½ cup Parmesan and ½ cup asiago. 
17. Bake until golden, about 20 minutes. 
18. Sprinkle with ½ cup Parmesan and ½ cup asiago. 

Adapted from a recipe by The Flavor of Bon Appetit 1999.