1. In a sturdy re-sealable plastic bag, combine the vinegar with 1/2 cup of the olive oil and the rosemary. Add the steak, seal the bag and refrigerate overnight, turning the bag several times.
2. Preheat the oven to 425° and bring the steak to room temperature. Heat a grill pan. Remove the steak from the marinade and season with the salt and pepper. Rub the side with the remaining 2 tablespoons of olive oil. Grill over moderately high heat until nicely charred on the top and bottom, about 5 minutes per side. Transfer the steak to a rimmed baking sheet and roast for about 30 minutes, until an instant-read thermometer inserted into the tenderloin (the smaller section) registers 125°. Alternatively, build a fire on one side of a charcoal grill or light a gas grill. Grill the steak over moderate heat for 5 minutes on each side. Transfer the steak to the cool side of the grill, close the lid and cook for 30 minutes longer. Transfer the steak to a carving board and let rest for 10 minutes. Slice the steak across the grain and serve immediately.