If using canned green peppercorns, strain them and crush about one half of them with a heavy knife. Set aside. Soak the porcini mushrooms for about 20 minutes, then strain. Set aside.

          Heat a medium heavy-bottomed sauté pan until hot. Add the butter and olive oil, then stir in the shallot and onion. Cook for one minute, then add the white, brown and porcini mushrooms to the pan. Add the peppercorns, salt and parsley and cook 4-5 minutes. Turn up the heat and add the white wine stirring until the wine evaporates. Reduce the heat and add the mustard and cream and stir slowly until smooth and creamy. Add the steak to the sauce and cook to your preference. Remove from the pan and slice thinly on the diagonal. Place on a warm serving platter.

         Turn up the heat under the sauce and bring almost to the boil add the Cognac and stir until it flames. Carefully pour the flaming sauce over the steak. Garnish with the parsley and sliced shiitake mushrooms.