For the lamb, first blend the rosemary and salt together in a food processor until mixed.
In a stand mixer fitted with the dough hook, mix together the flour and salt, then add the egg whites. Slowly add up to 300ml/10½oz water, but you may not need all it.
Once it comes together in a dough, knead it using the machine for about five minutes.
Remove the dough from the mixer, wrap in cling film and allow to rest for two hours.
Preheat the oven to 150C/300F/Gas 2.
Roll out the salt dough into a rectangle about 1cm/½in thick. Cut into four equal rectangles.
In a food processor, blend the garlic cloves to a paste with around 50ml/2fl oz water.
Brush the garlic purée all over the lamb shanks.
Wrap each lamb shank in a piece of dough with the bone sticking out of the top.
Place in a roasting tray and bake in an oven for 4½ hours. Remove the shanks from the oven and set aside to rest for 30 minutes.
Meanwhile for the pickling liquor, place all the ingredients except the cabbage into a saucepan and bring to the boil.
Remove from the heat and infuse for 30 minutes.
Strain the liquor through a sieve into a bowl and leave to cool.
Place the cabbage into the pickle mix and leave for at least an hour.
For the salad, mix the onions together with the chilli, sprinkle with the sea salt and set aside for 20 minutes.
Drain the pickled cabbage and mix the cabbage with the onion salad. Sprinkle with the chopped chives and drizzle with rapeseed oil.
For the mayonnaise, place all the ingredients except the oil into a food processor and blend to a fine purée. Gradually add the vegetable oil, while the food processor is running, until the mayonnaise has thickened. Season with a little salt.
To serve break open the crust around the lamb and serve each lamb shank with the pickled cabbage salad and mustard mayonnaise. Garnish with the nasturtium leaves.