Preheat oven to 140ºC. Prepare all ingredients to the specifications above.
Use a paring knife to poke approximately 20 small holes in the lamb shoulder and push a slice of garlic and half an anchovy into each hole. Rub a good amount of olive oil, a generous pinch of salt and the Sumac Pepper over the lamb.
Place a roasting tray on the stove top over medium heat and add a splash of olive oil. Add the onion wedges and brown slightly, then add the halved garlic cloves, lemon peel and thyme sprigs, before placing the lamb shoulder on top. Pour in the white wine and bring to the boil, cover the tray with a lid or foil and transfer to the oven. Cook for 3 hours at 140º C, then increase heat to 200º C, removing lid or foil and cooking for a further 30 minutes to brown the lamb.
Remove the meat from the tray, wrap loosely in foil and rest for 20 minutes. Place tray with onions and lamb juices on the stove over medium heat and cook for about 5 – 10 min. to reduce. Remove the thyme twigs from the mix and discard. Remove the lemon peel and finely slice, then return to the tray. Finely slice the silverbeet stems, add to the pan and cook for about 5 – 10 min. until softened, then add the sliced silverbeet leaves and olives and toss until warmed and wilted.