Pre-heat the oven to 150C / 300F.
Season the lamb with salt & pepper.
Heat olive oil in a large flameproof casserole dish over a high heat. Brown the meat a few cubes at a time on all sides, stirring frequently. Set aside while you sear the rest of the lamb.
Lower the heat to medium. Add the carrot and celery to the pan and cook for around 5 minutes, stirring frequently.
Now return the meat to the pan and add the passata and water, scraping up any bits stuck to the bottom (this will add flavor to the sauce). Bring to the boil.
Add the remaining ingredients. Bring back to the boil.
Put on the lid and transfer to the oven for around 2.5 hours (longer will not hurt).
Before serving, remove the parmesan rind and pancetta. Use a wooden spoon to break up the lamb and stir to form and nice thick ragu.
Serve over pasta (rigatoni or parpadelle are favorites) and sprinkle with parmesan and chopped fresh parsley.