Heat the olive oil in a flame-proof casserole pan and cook the pork, turning occasionally, until it is golden brown all over, about 10 mins. You need plenty of space in the pan, so cook in 2 batches if the meat starts to steam. Remove from the pan to a plate. Tip out any burnt bits, then add the butter and cook the onion for 3-5 mins until softened.
Stir in the flour, then return the pork and juices to the pan. Pour over the wine and enough stock to cover the meat. Bring to the boil, reduce to a simmer, put the lid on and cook for 45 mins, stirring occasionally. Tip in the prunes, top up with stock or water if the meat isn’t covered, and cook 45 mins more, uncovered, until really tender. Serve sprinkled with parsley.