Fish Stew with Rouille

Instructions:

Twist the heads from the prawns, then peel away the legs and shells, but leave the tails intact. Devein each prawn. Fry the shells in 1 tbsp oil for 5 mins, until dark pink and golden in patches. Add the wine, boil down by two thirds, then pour in the stock. Strain into a jug, discarding the shells. Heat the rest of the oil in a deep frying pan or casserole. Add the fennel, onion and garlic, season, then cover and gently cook for 10 mins until softened. Meanwhile, peel the potato and cut into 2cm-ish chunks. Put into a pan of cold water, bring to the boil and cook for 5 mins until almost tender. Drain in a colander. Peel a strip of zest from the orange. Put the zest, star anise, bay and ½ tsp harissa into the pan. Fry gently, uncovered, for 5-10 mins, until the vegetables are soft, sweet...