01 - Preheat your oven to 400°F (200°C). Lightly grease a 9x13-inch baking dish.
02 - In a large pot, bring salted water to a boil. Add diced potatoes and cook for 8–10 minutes, until just fork-tender. Drain and set aside.
03 - While potatoes cook, steam broccoli florets for 3–4 minutes until bright green and slightly tender.
04 - In a large mixing bowl, combine cooked potatoes, steamed broccoli, chicken, onion, and garlic.
05 - In a separate bowl, whisk together sour cream, milk, butter (melted), 1 cup cheese, salt, pepper, paprika, and thyme until smooth.
06 - Pour the creamy mixture over the potato, chicken, and broccoli mixture. Stir gently to coat everything evenly.
07 - Transfer the mixture to the prepared baking dish. Sprinkle the remaining ½ cup cheddar cheese on top.
08 - Bake uncovered for 25–30 minutes, until the casserole is bubbly and golden.
09 - Let rest 5 minutes before serving.