Prepare the Oven: Set the oven to 375°F. Lightly grease a baking dish so nothing sticks during baking.
Cook the Broccoli: Bring a pot of salted water to a boil. Add the chopped broccoli and cook just until tender. Drain well and set aside. This keeps the broccoli soft but not mushy.
Make the Sauce: In a bowl, stir together the cream of chicken soup, sour cream, milk, salt, and pepper. Mix until smooth and creamy with no lumps.
Layer the Base: Spread the cooked broccoli evenly across the bottom of the baking dish. Add the cubed chicken on top, spreading it out so every bite gets some.
Add the Sauce: Pour the sauce over the chicken and broccoli. Use a spoon to gently spread it so everything gets coated.
Add Cheese and Topping: Sprinkle shredded cheddar cheese over the top. In a small bowl, mix breadcrumbs with melted butter, then scatter it evenly over the cheese.
Bake Until Bubbly: Place the dish in the oven and bake for 30 to 35 minutes. The top should turn golden and the edges should bubble.
Rest Before Serving: Let the casserole sit for about 5 minutes before serving. This helps it set and makes scooping easier.
