Heat the oil in a large saucepan and sauté the onions, covered, until softened. Add the toasted nuts, sultanas, anchovies, water, tomato purée and oregano, and the saffron water if used. Cover and simmer for 20 minutes.
Meanwhile, separate the cauliflower into florets, if necessary, as evenly as possible. Drop into a large saucepan of rapidly boiling salted water and boil until just ten