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.