

Put the salt beef in a pan and cover with cold water. Bring to the boil, cover and simmer for 2 hours or according to pack instructions.
Remove from the pan and leave to rest, loosely covered with foil. Meanwhile put the potatoes in a pan of cold water, bring to the boil, cover and simmer for 15 minutes.
Add the leeks and curly kale, cook for a further 5 minutes, then drain well and return to the pan. Add the butter and mustard and mash really well. Season to taste.
Thinly carve the beef and serve on the mash with a dollop of horseradish sauce.