Lamb in Pastry with Mint Bearnaise

• 1 large loin of lamb
• 225 g (8 oz) shortcrust pastry salt
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Ask your butcher to remove the ‘eye’ of the lamb and the fillet from the loin. Remove any gristle and fat.

Preheat the oven to 230°C/450°F/Gas Mark 8.

Make the mushroom duxelles by sauteing the onion in the butter until soft and transparent. Add the mushrooms and cook u