1. Season and brush the steaks all over with oil.
2. Brush the grill bars with oil, place the meat on the hottest part of the grill, moving the steaks so that a criss-cross effect is marked on both sides. Then move them to a heat zone that will enable them to cook to the desired degree without burning.
3. Serve neatly arranged on a dish. Garnish with the straw potatoes and watercress and serve the sliced parsley butter separately in a sauceboat on a little crushed ice.