Preheat your oven to 350°F (175°C).
Boil egg noodles in a large pot according to package directions until al dente. Drain and set aside.
In a large mixing bowl, combine the cream of chicken soup, sour cream, chicken broth, garlic powder, onion powder, salt, and black pepper. Whisk until smooth.
Stir in the cooked chicken, cooked egg noodles, and frozen mixed vegetables into the soup mixture. Mix well until everything is evenly coated.
Transfer the mixture to a greased 3-quart baking dish and spread evenly.
In a separate bowl, mix the crushed cornflakes or breadcrumbs with the melted butter. Sprinkle the mixture evenly over the casserole.
Top with the remaining cheddar cheese.
Bake in the preheated oven for 30-35 minutes, or until the casserole is bubbly and the topping is golden brown.
Remove from the oven and let it cool for a few minutes before serving.