Transfer the roast to a rack in a shallow baking pan. Put the baking pan into a preheated oven. After 60 to 90 minutes of cooking, add the vegetables to the pan. Cook uncovered for a total of 2 1/2 to 3 hours, or until an instant-read meat thermometer reaches 135 degrees for medium rare.fter 60 to 90 minutes of cooking, add the vegetables to the pan. Cook uncovered for a total of 2 1/2 to 3 hours, or until an instant-read meat thermometer reaches 135 degrees for medium rare.