Trim the excess fat and sinew off the steaks. Combine all the marinade ingredients, except the olive oil. Place the t-bone steaks in a mixing bowl then pour the marinade over, turning to coat both sides. Cover and allow to marinate overnight in the refrigerator.
Just before grilling, add the olive oil and mix well. Place the steaks on a preheated barbecue grill and cook for about two to three minutes each side to seal in the juice.
For a rare steak, cook a further one to two minutes for each side. For a medium-done steak, cook a further two to three minutes for each side while for a well-done steak, cooking time is four to five more minutes.
Top steaks with a dab of butter after grilling. Serve with fried potato wedges and barbecued cherry tomatoes.