In a bowl cream together the cheese and the butter until the mixture is smooth. In a saucepan boil the wine with the peppercorns until it is reduced to about 1 tablespoon, add the cream, and boil the liquid until it is reduced by half. Reduce the heat to moderately low, whisk the cheese mixture, a little at a time, into the cream mixture, and whisk in the parsley. Remove the pan from the heat and keep the sauce warm.
Heat a well-seasoned ridged grill pan over moderately high heat until it is hot and in it cook the steak, patted dry and seasoned with salt and pepper, for 4 to 5 minutes on each side for medium-rare meat. (Alternatively, the steak may be broiled under a preheated broiler about 4 inches from the heat for the same amount of time.) Let the steak stand on a cutting board for 10 minutes and serve it, cut into thin slices, with the sauce and garnished with the watercress.
recipe courtesy of Gourmet magazine