Rub olive oil into the lamb and sprinkle with salt, pepper, dried garlic and rosemary. Place into a roasting tin and bake in the preheated oven for 30 minutes.
Heat olive oil in a saucepan and fry the onion and the garlic until soft. Add the tomatoes and sugar followed by the red wine. Bring to the boil, reduce the heat and let simmer until slightly reduced, about 10 minutes.
Remove the lamb from the oven and cover in the sauce.
Wrap in foil and place back in the roasting tin to prevent spills. Put in the oven at 90 C / Gas 1/2, or the lowest possible oven temperature, for 6 to 7 hours.