Generously season the pork on all sides. Heat the olive oil in a saucepan that is just large enough to hold the pork. Brown the meat on all sides , then remove. Discard the fat.
Melt the butter in the pan and add the garlic with the sage leaves. Before the garlic begins to colour return the pork to the pan.In a separate pan heat the milk to warm but not boiling.
Add enough milk to come three quarters of the way up the pork and bring gently to the boil. Add the lemon rind and reduce the heat. Cover the pan with a lid , slightly askew, and simmer very slowly for about 2 hours without disturbing.
When the pork is cooked the milk will have curdled to beige nuggets. Carefully remove the meat, slice quickly and spoon over the sauce.