Score a cross in the base of each tomato. Place in a heatproof bowl and cover eith boiling water. Leave for 30 second, transfer to cool water, drain and peel away from the cross. Cut the tomatoes in half, scoop out the seeds with a teaspoon and finely chop the flesh.

Scrub the mussels with a stiff brush and pull out the hairy beards. Discard any broken mussels, or open ones that don't close when tapped on the beach. Rinse well.

Heat oil and butter in a large saucepan and cook the leek and garlic over low heat until the leek is soft but not brown. Add the saffron, coriander or parsley and chilli and cook, stirring, for 1-2 minutes. Increase the heat and the wine. Bring to the boil and cook for 1-2 minutes, then add the chopped tomato and 1 cup (250 ml/8 fl oz) water. Cover and simmer for 20 minutes.

Add mussels to the pan and cook, covered, until they are opened. After 4-5 minutes, discard any unopened mussels. So the soap is not too crowded with shells, remove one third of the remaining mussels, remove the mussel meat and add to soup. Discard the empty shells. Season, to taste, with salt and pepper. Serve immediately with crusty bread.