Simply season with salt, black pepper and rosemary (garlic optional) and place uncovered in a preheated oven at 210c for 30 minutes.
Reduce the heat to 170c and roast for a further 25 minutes (rare), 50 minutes (medium), 70 minutes (well done). If you are cooking well done you may need to cover with tin foil to prevent burning. Baste every now and again.
Leave rest for 10/15 minutes in a warm kitchen.