Preheat the oven to gas 7, 220°C, fan 200°C.
Slash the fat of the lamb with a sharp knife and make incisions in which to poke wedges of garlic and rosemary sprig pieces.
Put the onion, celery and carrot pieces in the bottom of a large roasting tray.
Rub the lamb all over with oil and season with salt and pepper. Lay it on top of the vegetables in the tray and cover the tin with foil.
Roast in the preheated oven for 20 minutes, until the exterior of the lamb is well browned, then turn the oven down to gas 3, 160°C, 150°C fan. Pour the stock and wine over the lamb and recover tin. Return to the oven for another 3-4 hours, until the lamb is falling off the bone.
Take out of the oven and put the lamb to rest on a carving tray and keep the vegetables warm while making the gravy.
Pour off the excess fat from the roasting tray and pour the cooking juices into a jug. Place the roasting tray over a medium heat and add the flour and anchovies. Stir and scrape the bottom of the pan for 1 minute, then remove from the heat. Gradually stir in the cooking juices and then return to the heat, stirring continuously, as the gravy comes to the boil. Simmer until thickened and slightly reduced. Finally, stir in the capers and mint sauce.
The lamb should fall off the bone after 4 hours of cooking. Serve it with the gravy and some green vegetables.
*Inspired by Laura P. featured in the Realfood Cookbook
For top tips on protecting you and your family when preparing raw meat and poultry, visit Food Safety in the Home.