Preheat & Prep: Preheat oven to 400°F.
Cook Broccoli: Bring a large pot of water to a boil. Add broccoli and cook for 2-3 minutes until tender-crisp. Drain thoroughly.
Mix Sauce: In a bowl, combine 1 cup cheddar cheese, condensed soup, sour cream, milk, and seasonings.
Assemble Casserole: Stir in the drained broccoli and chicken, then transfer to a 9×13-inch casserole dish. Sprinkle the remaining cheese on top.
Prepare Topping: In a small bowl, mix melted butter with breadcrumbs, then sprinkle over the casserole.
Bake: Place in the oven and bake for 18-20 minutes until the top is golden brown and bubbly.
Serve: Enjoy on its own or over rice, noodles, or mashed potatoes.