Place 1 tbsp of the lard or oil in a flameproof casserole over a medium high heat . When hot, add the sausages and brown them all over for 8-10 minutes. Do this in batches if necessary. Set aside on a plate.
Add the renaining tablespoon of fat to the pan. When hot, add the leeks and cook over a medium low heat for about 5 minutes until soft.
Sprinkle over the flour and stir for a minute. Pour in the stout, bring to the boil and let it bubble for a couple of minutes. Add the stock, prunes and lentils then return the sausages to the dish. Add a small pinch of salt and a sprinkle of pepper.
Bring to the boil then simmer, uncovered, for 25-30 minutes or until the lentils are tender, stirring occasionally. If the dish is too salty add a squeeze of lemon or a pinch of demerara sugar.
Scatter the parsley over the dish and serve with some mashed potato.