First put the kettle on to boil, then after soaking the kidneys, slice them across into 1/4 inch (5mm) thick medallion-shaped slices and snip out the white cores using a pair of scissors.
Now transfer them to a sieve and rinse them with a kettleful of boiling water; leave them to drain thoroughly and dry them in some kitchen paper. Next, in a cooking pot, melt the lard and soften the onion and garlic in it for 5 minutes. Then turn the heat up to high, add the drained and dried kidneys and brown them on all sides. Next lower the heat and stir in the flour to soak up the juices before adding the stock, cider, thyme and seasoning.
Now put a lid on and simmer gently for 45 minutes. Meanwhile, mix the mustards with the cream, add a pinch of cayenne pepper, then stir this into the cooked kidneys. Cook for a minute or two, then serve with buttered noodles or rice.