Start by preparing the mash. Peel the potatoes, place into a pan, cover with water, season with salt and boil for about 15 minutes until soft. Meanwhile in a small frying pan cook the diced leeks and black pudding in the butter.
Drain the potatoes and mash with a potato ricer directly into the pan with the leek and black pudding. Mix well and season if required. Divide the mixture into 8 equal amounts and shape into fishcakesized rounds. Pat down with a palette knife so they are even all over. Set in the fridge for 30 minutes until firm.
Place the beaten egg, flour and breadcrumbs on three separate plates. Dip each potato cake in the flour first, then the eggs and finally the breadcrumbs. Shallow fry the cakes in a little oil and then keep warm.
Heat a tablespoon of oil in a pan and gently pan fry the sausages with the sage, onion rings and garlic. When the sausages are cooked through and golden brown remove to one side, then add the cider to the pan and allow to boil to reduce the liquid slightly. Finally add the pork stock to create a tasty gravy. Serve the sausages with the cider gravy, potato cakes and a little sprig of watercress to finish.