Heat 1 tablespoon oil in a frying pan and fry the leeks for 3-4 minutes. Transfer to a casserole dish.
Heat the remaining oil and brown the pork, add the oats, stock cube, 200ml water, cider and mustard, bring to the boil. Stir into the leeks and add the sage. Cover and bake for 1 hour until the meat is tender.
Try adding some cannellini beans towards the end to help the meat go further.