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.op round roasts come from the hind quarter of the steer, and those muscles get well worked. Consequently, top round roasts are lean and full-flavored, but lacking fat and marbling, they don’t tenderize quickly. Cook your top round oven roast slowly with a low heat.