Cut the liver into thick strips, removing any tubes. Season the flour with salt and pepper and use to coat the liver. Cut the bacon rashers in half and wrap a piece around each prune.
Heat half the oil in a flameproof casserole and fry the onions until lightly browned. Drain to a plate. Add the liver to the casserole and brown on both sides. Drain to the plate. Add the remaining oil to the pan with the bacon-wrapped prunes and fry on both sides until browned. Drain.
Arrange the potatoes in the casserole and put all the fried ingredients on top. Pour the stock over, season lightly and bring to the boil. Cover with a lid and transfer to a preheated oven, 180°C (350°F), Gas Mark 4, for 50 minutes until the potatoes are very tender. Serve sprinkled with the parsley.