Marinate the steak in the Worcestershire sauce and the olive oil for at least 30 min (a couple of hours would be better).
Cut the potatoes into large wedges and place them in a roasting pan together with the rosemary and garlic cloves, drizzle extra virgin olive oil and sprinkle liberally with sea salt and freshly ground black pepper.
Roast the potatoes in a hot oven (200ºC) for about 30 minutes or until the wedges are golden brown and thoroughly cooked. Remove the steak from the marinade, season with the salt and pepper, then place on a cleaned grid over a fairly fierce heat and grill until rare to medium done or as preferred.
Remove steak from the grill and rest for 5 min. slice steaks across the grain and arrange on a plate or platter with a big pile of potato wedges and lashings of béarnaise.
Reduce the verjuice, dried tarragon, tarragon vinegar, green peppercorns and onion together until about 40ml is left.
Combine the reduction and the egg yolks in a stainless steel or glass bowl over a double boiler. Whisk the mixture until it reaches the ribbon stage. Remove the emulsion from the heat and slowly whisk in the melted butter. If the mixture seems a little thick add a couple of tablespoons of hot water.