Cook the fish for about 30 minutes in a quantity of water large enough to cover the fish, and containing the following ingredients: salt, pepper, a bay leaf, the lemon juice and the onion cut in half. When cooked, remove the fish from the water and drain. Remove the skin, head and bones and cut the fish into small pieces.

Prepare mayonnaise with 2 egg yolks and olive oil. When it is ready slowly add the juice of 1/2 a lemon. Mix the mayonnaise with the sliced gherkins, peeled and cubed potatoes, the chopped parsley and scallions. Pour this over the fish. Decorate with the black olives, thin lemon slices and 3 sliced hard-boiled eggs.