Place the oil, red wine, rosemary and garlic in a shallow dish and whisk together. Add the steaks and turn to coat. Cover and marinate for 2-3 hours in the fridge.
Meanwhile, mash the butter with the parsley and chopped olives using a fork. Season lightly then place on a piece of parchment paper to form a cylindrical shape. Roll up, twist the ends to seal and chill.
Preheat a barbecue or griddle pan to hot. When ready, place the steaks on the barbecue or griddle and cook for 3-4 minutes on each side for a medium steak, or 5-6 minutes for well done.
Cut the butter into 8 thin slices and place 2 slices on top of each steak. Remove the steaks from the heat when the butter starts to melt. Serve with new potatoes and a rocket and sliced radish salad.
The butter can be made in advance. Keep in the fridge until ready to use. You could add a crushed clove of garlic or other fresh herbs to the butter.
