Preheat the oven to 350°F (180°C).
In a large mixing bowl, combine the cooked chicken, egg noodles, cream of chicken soup, sour cream, mayonnaise, milk, poppy seeds, and Parmesan cheese. Ensure all ingredients are thoroughly mixed together.
Spread the mixture evenly into a 9×13-inch baking dish that has been greased.
In a separate small bowl, blend together the crushed cornflakes and melted butter. Spread this mixture evenly over the top of the casserole.
Bake the casserole in the preheated oven for approximately 35-40 minutes, or until it becomes hot and bubbly.
Serve the casserole while hot, optionally garnishing with additional poppy seeds for added flavor and visual appeal. Enjoy the delicious combination of flavors in each bite!