Preheat oven to 190 degrees C. Grease an 20x20cm baking dish.
Place the cauliflower into a microwaveable dish, and microwave on High 3 to 4 minutes, until tender. Place the cooked cauliflower into the baking dish, sprinkle with Cheddar cheese and couscous, and dust the top with nutmeg.
Bake in the preheated oven for 12 to 15 minutes, until the top of the casserole is golden brown, and the cheese is melted. Stir in butter to taste.