Heat oven to 350F. In a roasting pan or on a rimmed baking sheet toss the potatoes, tomatoes, 3 tbs of the oil 1/2 tsp salt and 1/4 tsp pepper.
Season the beef with 1 tsp salt and 1/2 tsp pepper. Nestle it in the middle of the pan among the vegetables.
In a small bowl, combine the garlic, rosemary and remaining tbsp oil and rub it evenly over the meat. Roast the meat to the desired doneness, stirring the vegetables once, about 1 hour 15 minutes for medium-rare (when meat thermometer registers 130F) let rest 10 minutes before slicing.