Remove any remaining parts of skin and the central bone. Put these discarded parts in a small saucepan with salted water and simmer them for about 10 minutes; filter and you’ll have stock to add to the linguine when you toss them with the sauce. Cut the flesh of the monkfish into pieces and chop them in the food processor. Coarsely chop the carrot, parsley and celery together, then sauté them with 3 tablespoons of olive oil in a heavy bottomed frying pan (large enough to contain the pasta as well). Add the chopped monkfish, stir well and, after 5 minutes, add the white wine and let it evaporate over a lively heat. Season with salt and pepper to taste (Pier Filippo always gladly volunteers to try it), lower the heat and continue cooking for roughly 15 minutes. In the meanwhile, break up the walnuts and sauté them in a small pan with a tablespoon of olive oil and the grated rind of the orange. Cook the pasta in plenty of boiling, salted water, strain it when its “al dente” and toss it in the frying pan with the fish sauce. Add the mixture of walnuts and orange rind, pour in a ladle of fish stock and stir everything thoroughly. Finish off the linguine with a few leaves of parsley and a “drizzle” of extra virgin olive oil, and serve while hot.