Using a greased large oblong or square baking dish, layer bottom with 1/2 of hash brown patties. Top with 1/2 cheddar cheese and mozzarella cheese. Add 1 tablespoon of sour cream on top of each hash brown. Evenly top with chicken, broccoli and onion. Layer remaining hash browns. Top with remaining cheese and add 1 tablespoon of sour cream on each hash brown.
Mix: milk and cream of celery soup. Pour evenly over potatoes. Do not let it cover the potatoes completely (almost covers). Sprinkle with paprika.
Bake at 350°F for 45 minutes, longer if you desire the top to be extra crispy.