Kidneys with Mustard Cream & Celeriac Mash

Mustard is a larder staple that goes wonderfully with liver or kidneys. The most famous French mustard is from Dijon, and is traditionally a smoother mustard that goes well with pork, veal or steak. For this dish, I would go for a wholegrain one, to give a bit of bite to the smooth kidneys. This is a hearty, cheap and robustly flavoured dish. You can replace the kidneys with liver, pork chops or beef skirt if you like.