Begin by making the salsa verde. Finely chop the capers, herbs and watercress, then mix them in with the anchovy fillets, crushed garlic, olive oil, mustard, lemon juice and black pepper.
Light a barbecue for direct cooking. Begin cooking when the flames have significantly lowered and the coals are covered in a layer of white-grey ash.
Brush the steak on both sides with oil and season heavily with salt and pepper. Turn frequently on the grill – every 30 or seconds or so – until it has cooked for about 3 minutes on both sides.
Remove the steak from the heat and place on a plate, cover loosely with foil then leave to rest for 5 minutes before slicing. Add the salsa verde to serve.
Recipe courtesy of www.greatbritishchefs.com