Capuchin-style Salt Cod

Clean and wash the salt cod, dry it and cut into regular pieces. Put into a casserole covered with cold water. Bring to the boil, then lower the heat and simmer gently for about 12 minutes. Take the pieces out, eliminate the skin and bones, divide the flesh into thin sheets and put aside. Slice the onions, blanch them for 8 minutes, and toss them into a pan in which a piece of butter and the oil are frying. Cook the onions until they are almost coming apart. Then, in a constant rain, very slowly, incorporate the flour, and, stirring well, add the boiling milk little by little. Season with a pinch of pepper, a little nutmeg, salt (if necessary) and chopped parsley. Bring to the boil and then lower the heat. At this point, add the sheets of salt cod and leave to cook over moderate heat for 25 minutes. Transfer the salt cod to an oven-dish, even up with the back of a tablespoon and sprinkle with grated Parmesan, mixed with a few breadcrumbs. Drizzle with melted butter. With a pastry bag, decorate the rim of the oven dish with duchess potatoes. Put the pan into the oven. As soon as the mixture is nicely golden and the surface of the fish browned, serve.