Remove the bones, gristle and some of the fat from the cooked lamb while it is still warm, and cut into neat fingers or squares when cold. Mix the melted butter with the beaten egg, thyme and seasoning. Dip each piece of lamb into this mixture, then into fresh breadcrumbs.
Grill under a moderate heat until browned both sides, and serve with Béarnaise or tomato sauce. They make crisp lit