My Secret Chicken Divan Chicken and Broccoli Proper Supper

Ingredients

• 4 cups Cooked Chicken Breast or Thighs, shredded or diced
• 1 lb Fresh Broccoli Florets (or frozen, thawed and drained)
• 1 tablespoon Olive Oil
• ½ teaspoon Kosher Salt
• ¼ teaspoon Black Pepper
• 4 tablespoons Unsalted Butter (for sauce)
• 4 tablespoons All-Purpose Flour
• 2 cups Whole Milk, warmed slightly
• 1 cup Chicken Stock (low sodium)
• ½ teaspoon Onion Powder
• ¼ teaspoon Ground Nutmeg
• 1 teaspoon Dijon Mustard
• 2 tablespoons Dry Sherry or Fresh Lemon Juice
• 1 cup Shredded Sharp Cheddar Cheese
• ½ cup Shredded Gruyère or Swiss Cheese
• Salt and White Pepper, to taste
• ½ cup Panko Breadcrumbs
• ¼ cup Grated Parmesan Cheese
• 2 tablespoons Unsalted Butter, melted (for topping)