Place tomatoes, onion, garlic, wine and rosemary in a heavy pan. Put lamb on top and brush with olive oil. Cover tightly with foil and cook for 3h at 150°. Turn the lamb and cook for another hour. Remove the foil. Turn the lamb again, brush liberally with sweet chilli sauce and cook for another 1/2h. Remove the lamb and keep warm. Squeeze the garlic into the sauce and thicken with some plain flour (and water) if necessary.