Preheat oven to 400 F
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, Sour Cream, Dry Sherry, Colonel Pabst Worcestershire Sauce, Soup and 1/2 cup cheese, stirring until well combined.
Add Mayonnaise mixture to Broccoli mixture; stir gently until combined.
Spoon mixture into 9×13 inch baking dish coated with cooking spray.
Sprinkle with remaining 1/2 cup of Cheese.
Bake at 400 F for 50 minutes or until mixture bubbles at the edges and Cheese begins to brown.
Remove from oven let cool on wire rack 5 minutes