1. Preheat your oven to 375°F (190°C). Lightly grease a 9×13 inch baking dish.
2. Bring a large pot of salted water to a boil. Add the potato cubes and cook until tender, about 10 minutes. Drain well.
3. In the same pot, blanch the broccoli florets for about 3 minutes, then drain.
4. In a large bowl, mix the sour cream, milk, half of the cheese, garlic powder, and onion powder. Season with salt and pepper.
5. Add the cooked potatoes, chicken, and broccoli to the sour cream mixture and stir to combine. Transfer the mixture to the prepared baking dish.
6. In a small bowl, mix together the breadcrumbs and melted butter. Sprinkle over the casserole along with the remaining cheese.
7. Bake in the preheated oven for 20-25 minutes, or until the top is golden brown and bubbly.
8. Let the casserole stand for 5 minutes before serving to let it set.
