Sear the trimmed and tied joint in hot oil before roasting to seal and brown the outside, then insert a meat thermometer, making sure the tip of the spike is in the centre of the meat.
A 1.5 kg beef fillet roasted at 220°C should take about 20 minutes for rare meat, 25-30 minutes, medium-rare.
Season joint, then sear in hot oil, turning with tongs. Insert thermometer and place in preheated oven.
Baste frequently during roasting to keep meat moist. Check thermometer reading; remove from oven.