Bring the prawn heads and shells, fish bones, stock, wine, water, the half onion, 10 ml of the garlic and 1 bay leaf to the boil in a large pot.
Reduce the heat and simmer for 20 minutes. Strain the mixture through a sieve and reserve the stock.
Heat the oil in a large pot and add the remaining onions and garlic and the leek. Cover and sauté or 10 minutes over low heat or until the onions are soft but not brown. Stir occasionally.
Add the tomatoes, tomato paste, saffron or turmeric, the remaining bay leaves, basil, fennel seeds, orange peel, salt and pepper.
Stir well and boil uncovered for 10 minutes, stirring
frequently. Add the strained stock, bring to the boil and boil rapidly for 10 minutes, stirring frequently.
Reduce the heat, add the fish and mussels, cover and simmer for 4-5 minutes. Add the prawns, cover and simmer for another 3-4 minutes, taking care not to overcook the prawns.
Remove the orange peel and bay leaves and serve hot as a soup or stew with tomato chutney.