Preheat oven to 425 F.
Place florets in lg microwave-safe prep bowl. Add approx. 1" water.
Microwave cauliflower on High to soften, approx. 3 min. Drain.
Place cauliflower in 13x9" glass baking dish. Dot with butter cubes. Sprinkle with za'atar.
Bake at 425 F until tender and browning, approx. 45 min.