• 5 pounds mussels (there should be about 12 mussels in a pound)
• 2 large onions, chopped
• 5 tablespoons water
• about 1 teaspoon salt
• 2 garlic cloves, chopped
• freshly ground black pepper
• 1 egg yolk
• ¾ cup oil (half olive oil, half peanut oil)
• 1 tablespoon Dijon mustard
• juice of half a lemon
• ½ cup minced Italian parsley

Scrub the mussels under cold water with a stiff brush and remove the beards. Let the mussels stand for 10 minutes in cold water and discard the mussels that either have opened shells or are very heavy.

Put the onions in a large frying pan with the water, salt, garlic, and pepper. Boil, covered, for 10 minutes. Add the mussels and cook, covered, for 4 minutes, stirring occasionally. Remove the mussels with a slotted spoon and discard the shells. Strain the liquid through a piece of cheesecloth spread over a sieve.

Prepare the sauce with the egg yolk, oil, mustard, and lemon juice (for instructions, see Mayonnaise). Add the parsley, then slowly stir in 2 to 3 tablespoons of the mussel broth. Pour the sauce over the mussels, sprinkle with parsley, and chill.