Wipe the meat and cut into round even fillets not less than ½ in. thick. Finely chop the mushrooms and shallot and mix well together with the parsley, salt and pepper. Place a round pat of this mixture in the centre of each fillet. Heat the fat in a sauté pan, put in the fillets with the stuffing side down, fry quickly, then turn and fry the other side a little more slowly. When cooked, arrange in a row on a foundation of spinach or mashed potatoes. Pour some sauce round the noisettes and serve the rest of the sauce separately.