Au Jus is just a fancy name for making a beef gravy without adding any flour or cornstarch for thickening. Our time-test results are based on a roast that was about 7-in (17.5 cm) long x 5-in (12.5 cm) wide x 4-in (10 cm) deep. NOTE: ‘Time-to-cook’ figures are rough guidelines only as cook time is dependent on so many factors such as: oven and thermometer accuracy, starting temperature of roast, roast shape and cut. A good thermometer is one of your best kitchen investments.