Soak the prunes overnight then cut in half and remove the stones. Cut the 3 pork into cubes and place in a 3-pint round casserole with the prunes and the peeled and sliced potatoes and onions. Season and add the stock. Cover and cook slowly for 1 and half hours at gas mark 3-325F (180C) until the meat is tender. Meanwhile prepare the stuffing mixture and form into small balls. Core and slice the apple. When the casserole is cooked add the stuffing balls and arrange the apple slices around the edge. Place in the oven until the apples are browned.