Heat the olive oil in a large pan. Add the onions, garlic, chilli, saffron and seasoning and soften over a gentle heat for 10 minutes. Add the chopped tomatoes, purée and white wine. Bring to the boil and simmer for 5 minutes to reduce some of the liquid.
Add the potatoes and simmer gently for 15 minutes.
Add the cleaned shellfish and then carefully lay the fish fillets on top. Cover with a lid and simmer for a further 10 minutes.
Just before serving, add lots of chopped parsley. Serve in large open soup bowls, with plenty of finger bowls at the table.