Soak the mussels in cold water for five minutes, and scrub to remove any dirt or sand. Change water several times.
3
Put the mussels into a saucepan, add garlic, parsley, onion, wine, vermouth and juice of lemon. Season generously, bring to the boil, cover and cook for about 5 minutes or until mussels are open. Shake the pan from occasionally. Add butter and stir through.
4
Note: discard any mussels that do not open.
5
Serve mussels in a bowl and pour over cooking liquid.