Heat the oven to 240C/220C fan/gas 9. Using a mortar and pestle, pound the garlic, lemon zest and half the herbs with a pinch of salt. Mix in the lemon juice and 1 tbsp oil. Pierce the leg of lamb all over with a knife and rub with the herb paste, getting into the slits.

Put the potatoes in a roasting tin and toss in the remaining olive oil plus any remaining herb paste. Nestle the lamb among the potatoes, roast for 20 mins, then reduce the temperature to 180C/160C fan/gas 4. Roast for 1 hr-1 hr 15 mins for medium-rare; add 15 mins if you prefer it medium and 10 mins more for well done. During cooking, baste the lamb once or twice with the juices and turn the potatoes. When the lamb is done, remove from the tin and leave to rest. Add the remaining herbs to the potatoes, remove from the tin and keep warm.

Scrape the roasting juices from the tin into a shallow pan. Add the chopped tomatoes, half a can of water, the stock cube and olives, then simmer gently for 10 mins. Serve the lamb with the potatoes, sauce, asparagus and a simple salad.