In a large pot over medium heat, melt butter. Add garlic and gently cook until soft then stir in nutmeg, pepper and salt and cook 30 seconds. Add the water and cauliflower. Bring to the boil, reduce heat, cover and simmer 20 minutes or until cauliflower is tender.
In a small saucepan over medium heat, cook carrot with water to cover until just tender. Drain and reserve.
Purée cauliflower soup in a blender or food processor. Add carrot, spring onion and parsley. Serve.