How to Make It
Preheat oven to 350˚F. Trim cauliflower into florets. Bring a large saucepan of salted water to a boil over high; add cauliflower, and boil until just tender, 4 to 5 minutes. Drain cauliflower, and return to saucepan.
Stir together cream of chicken soup and sour cream in a small bowl; add to cauliflower, and toss to combine. Transfer mixture to a greased (with cooking spray) 8-inch square baking dish. Sprinkle casserole with cheese and panko; dot with butter slices.
Bake in preheated oven until casserole is bubbly and panko is golden, about 30 minutes. If desired, top with parsley.