2. In a mixing bowl, toss the potatoes, carrots and parsnips together with the olive oil, rosemary, salt and pepper. Transfer the vegetables to a shallow roasting pan and roast them in the oven for 10 minutes.
3. Season the beef with salt and a generous amount of pepper. Remove the vegetables from the oven and place the beef on top of them in the roasting pan. Return the pan to the oven and roast the vegetables and beef for 15 minutes.
4. Turn the temperature down to 350ºF and continue roasting for an additional 15 minutes or until the vegetables are tender and the beef is cooked to the desired doneness. (To check for doneness, insert a meat thermometer into the thickest part of the roast. It should read 135º for medium rare.)
5. Let the tenderloin rest for 10 minutes before slicing. Serve a few slices of the beef with a large spoonful of the vegetables.