• 2.25 litres/2 quarts mussels
• 1 onion, finely chopped
• 3 dl/½ pint water
• 3 dl/½ pint dry white wine
• 25 g/1 oz butter
• 25 g/1 oz flour
• 1 egg yolk
• 2–3 tablespoons cream
• juice of½ lemon
• freshly milled pepper
• chopped parsley

Wash and scrub the mussels in several changes of cold water. Discard any with broken shells or ones that are not tightly closed. Pull away the beard from each one.

Rub the inside of a large saucepan with a buttered paper and sprinkle with the chopped onion. Put the clean mussels in the pan and add the water and wine. Cover the pan with a lid and place over high heat. Shake the pan occasionally and cook for 2–3 minutes or until the mussels have opened up. Remove from the heat, lift out the mussels and retain the liquid in the pan. Discard any mussels that have not opened up, then remove remaining mussels from the shells. Place in gratin dishes and keep hot while you make the sauce.

Carefully strain the liquid from the pan. Melt the butter in a saucepan over low heat and stir in the flour. Cook gently for 1 minute then gradually stir in the hot mussel stock. Bring up to the boil stirring well to get a smooth sauce. Cook gently for a few moments then draw off the heat. Stir in the mixed egg yolk and cream and lemon juice to taste. Check seasoning with pepper and reheat. Pour the hot sauce over the mussels. Sprinkle with parsley and serve.