Toss the veal shanks in the seasoned flour. Heat some oil in a large, heavy-based pan and cook the shanks until browned all over, then remove from the pan.
Heat more oil in the pan if necessary and add the onion, garlic, celery, carrot and a pinch of sea salt and cook over medium heat until the onion is soft. Stir in the olives, tomato paste, lemon and orange zests, wine, tomato and its juice, stock, bay leaves, thyme and browned shanks.
Simmer very slowly, covered, for 1 hour. Remove the lid and simmer uncovered for a further 45 minutes, or until the meat is falling off the bone. Check the seasoning and add more sea salt if necessary.
Place a spoonful of polenta on the side of four large bowls, spoon the shank mixture on and give a good grind of pepper and a squeeze of fresh lemon.