Boil the potatoes in their jackets and allow them to cool completely. (Day-old cooked potatoes that have been refrigerated work very well for this dish.) Peel the potatoes and cut them into 2cm/¾ inch dice.
Break up the cauliflower into chunky florets, about 4cm/1½ inches across at the head and about 4cm/1½ inches long. Soak the florets in a bowl of water for 3