Peel off the outer membrane, slice in half lengthways, and cut out the white core. Soak in a little cold milk for 30 mins before cooking, pat dry and cut into chunks. Devil your kidneys: take 6 kidneys, melt butter in a heavy bottomed pan and add thinly sliced onion, & fry until soft. Toss the kidneys in some seasoned flour and then add to the pan, lightly fry for 2-3 mins, add 1 tablespoon each of mustard and tomato puree, add 250 ml water and a tablespoon of Worcestershire sauce and stir well. Cook until it all thickens, & serve on buttered toast.