1 Bring the water to the boil in a large stockpot and add the bones, brisket and peppercorns. Reduce the heat to a ‘blip’ and simmer for 3-4 hours, skimming off any froth that comes to the surface.
2 An hour before the end of cooking time, add the vegetables and lovage and leave to simmer on a low heat.
3 When the meat is completely tender, remove from the pot. Carefully season the soup and strain. Discard the bones. Cut the beef across the grain into finger-thick slices and serve in a deep dish. Pour the hot stock over it and some of the tender vegetables if desired.
4 Mix together the horseradish and apple puree in equal quantities to serve alongside. Sprinkle the beef with sea salt and chives just before serving.