Skin and well wash the kidneys. Split open and remove the cores. Cut the kidneys into neat pieces. Melt the fat in a small pan, put in the onion and cook without browning. Then add the kidney, salt, cayenne, chutney, lemon juice, mustard and stock. Cover and stew for a short time over moderate heat until the kidney is cooked. Cool slightly and stir in the egg yolks. Sprinkle in enough breadcrumbs to make a soft consistency and correct the seasoning. Serve on buttered toast or in a mashed potato border.