Steak with Peppercorn Sauce (Steak au Poivre)

olive oil

approx 800g (2 lb) beef fillet, cut into 4 large medallions (see Kitchen Notes)

sea salt

freshly ground pepper

unsalted butter

shallots, finely chopped

brandy or cognac

chicken stock or beef stock

plus 2 teaspoons) double cream (heavy cream)

green peppercorns in brine, drained (or more, to taste)

cornflour (cornstarch)

parsley, finely chopped