Heat the oven to 220C/200C fan/gas 7. Remove all packaging from the lamb and keep a note of the weight to calculate the roasting time. Make incisions into the lamb using a small sharp knife, at an angle, about 5cm into the meat. Making the holes at an angle will mean more of the meat is flavoured, and the flavourings will be less tempted to be pushed out when roasting.

Insert a short sprig of rosemary, a garlic slice and a small piece of anchovy (if using) into each of the holes, pressing in well with your finger. Season the meat all over with salt and pepper, then rub the lamb all over with the olive oil. Transfer to a roasting tin, sat on the onion slices. Roast for 20 mins.

Lower the oven to 190C/170C fan/gas 5 and cook for another 15-20 mins per 500g (1 hr – 1 hr 20 mins for 2kg leg) depending on how pink you like your lamb. You can also check the internal temperature of the lamb if you prefer pinker meat – it will be 55C for medium (pink) and 70C for well done.

Cover with foil and rest for 15 mins before carving. Save the tray juices and onion slices to make gravy.