Bring the steak to room temperature for at least 30 minutes. Preheat your grill to high. Drizzle lightly with the olive oil. Season with salt and black pepper. Grill the steak for about 4 minutes on each side or more if desired. Transfer the steak to a plate, cover with foil and let rest. Melt the butter in a small pan. Add the mushrooms and saute for about 5 minutes over a medium-high heat and the mushrooms start to soften. Add the chopped rosemary and stir. Place the steak on a plate and spoon the mushrooms over the top. Pour any extra pan juices from the mushrooms over the steak also. Serve at once.
