1 Preheat oven to 160°C. Make several 2cm-deep slits in the top of the lamb and insert slices of garlic and pieces of rosemary. Put lamb in a small, deep ovenproof dish, pour over the chicken stock, cover with aluminium foil and cook for 2 hours. Remove the foil and cook for a further 45 minutes. Remove the lamb from the oven, cover with foil and stand until warm.

2 Heat the oil in a heavy-based pan over a medium-low heat and cook the onion for 10 minutes or until softened but not coloured. Add the sugar and water and stir until the sugar has dissolved. Add the vinegar and stir until combined. Bring to a simmer and cook, uncovered, for 30-35 minutes or until the onions are soft and caramelised. Spoon the onion mixture into a bowl.

3 Pull the meat from the bone and shred, using 2 forks. Cut the crusty white loaf into 2cm-thick slices and spread with butter. Pile the lamb on the buttered bread. Top with a spoonful of caramelised onion, season with freshly ground black pepper and cover with another slice of buttered bread.