In a large heavy-based saucepan on a high heat, warm the oil and add pork. Season with salt, colour lightly all over then remove from the pan and set aside.
Reduce temperature, then add onions and cook for about 10 minutes, until softened. Add garlic, celery, carrot and sage and cook for a further 5 minutes, then add the wine and allow to reduce until almost dry.
Now add tomatoes, bay leaves, thyme, both stocks and bring to the boil. Return pork to the pan, reduce heat to a simmer, cover with a lid and very gently cook for about 1½ hours. Simmer until the pork is tender and sauce has reduced, adding olives at the end.
Remove from heat, add pepper, lemon juice, zest and parsley. Adjust seasoning and serve with soft polenta.