Light Chicken Broccoli Casserole

3 quarts water
1 (12-ounce) package broccoli florets
4 (6-ounce) skinless, boneless chicken breast halves
1 (12-ounce) can evaporated fat-free milk
1/4 cup all-purpose flour (about 1 ounce)
1/4 teaspoon salt
1/4 teaspoon freshly ground black pepper
Dash of nutmeg
1 cup fat-free mayonnaise
1/2 cup fat-free sour cream
1/4 cup dry sherry
1 teaspoon Worcestershire sauce
1 (10.75-ounce) can condensed 30% reduced-sodium 98% fat-free cream of mushroom soup, undiluted
1 cup (4 ounces) grated fresh Parmesan cheese, divided

Preheat oven to 400°.

Bring water to a boil in a large Dutch oven over medium-high heat. Add broccoli, and cook 5 minutes or until crisp-tender. Transfer broccoli to a large bowl with a slotted spoon. Add chicken to boiling water; reduce heat, and simmer 15 minutes or until done. Transfer chicken to a cutting board; cool slightly. Cut chicken into bite-sized pieces, and add chicken to bowl with broccoli.

Combine evaporated milk, flour, salt, pepper, and nutmeg in a saucepan, stirring with a whisk until smooth. Bring to a boil over medium-high heat; cook 1 minute, stirring constantly. Remove from heat. Add mayonnaise, next 4 ingredients (through soup), and 1/2 cup cheese, stirring until well combined. Add mayonnaise mixture to broccoli mixture; stir gently until combined.

Spoon mixture into a 13 x 9-inch baking dish coated with cooking spray. Sprinkle with remaining 1/2 cup cheese. Bake at 400° for 50 minutes or until mixture bubbles at the edges and cheese begins to brown. Remove from oven; let cool on a wire rack 5 minutes