Season the meat. Heat the oil in a frying pan. Brown the meat all over for approx. 8 mins. over a medium heat, only turning when a crust has formed. Remove the meat, wipe the cooking fat from the pan and add a little oil.
Sauté the onions and garlic, then add the celeriac and half of the plums and cook briefly. Add the wine and all the other ingredients up to and including the cinnamon, bring to the boil, reduce the heat, return the meat to the pan. Cover and leave to braise over a low heat for approx. 2 hrs., turning twice. Remove the meat, cover and leave to rest for approx. 10 mins. Cook the sauce with the remaining plums for approx. 5 mins., season.