Pick over the mussels and discard any that are open and that don’t close when tapped. Put a large, heavy-based frying pan on a high heat. When the pan is piping hot and almost smoking, add the mussels with 25ml/1fl oz of water. Cover with a tight-fitting lid and cook for about 2 minutes, until the mussels have opened. Remove the pan from the heat. Pick through the mussels, discarding any that have not opened. Add the extra virgin olive oil, sherry vinegar and herbs, season with salt and pepper, and toss together well in the pan. Serve immediately in warmed bowls.