Hollandaise Egg Sauce Parisian--For Codfish

Combine 2 egg yolks and 2 teaspoons tarragon vinegar. Heat 1 tablespoon butter or 2 tablespoons olive oil in the top of a double boiler over hot but not boiling water. Whip in the egg yolks and cook the mixture, stirring constantly, until it has the consistency of thick cream. Season to taste with salt, pepper, and nutmeg. Remove the pan from the heat and stir in 1 hard-cooked egg, coarsely diced, and 1 teaspoon finely minced chervil. Old in 2 egg whites stiffly beaten, and serve the sauce arm.