Grind the thyme, pine, coriander seeds and rosemary in a spice grinder or pestle and mortar and mix until a fine-powder consistency.
Mix the spices with the salt in a large bowl. Coat the mutton pieces with the spices, cover with clingfilm and leave to marinate in the fridge for 24 hours.
Once the meat has marinated, rinse off the salt under cold water and then pat the meat dry with a paper towel.
Heat the oil in a frying pan on a high heat and fry the meat pieces for 2-3 minutes, or until the outer flesh is dark brown and starting to caramelise.
Put the meat into a pressure cooker and cover with chicken stock.
Heat the cooker until it reaches full pressure and cook for 45 minutes.
Remove the pressure cooker from the heat and strain the meat through a sieve, and gather the juices into a clean saucepan.
Heat the meat juices until the mixture is reduced by two-thirds, or can coat the back of a spoon.
Flake the meat using a fork. Add 150ml/5fl oz of the reduced stock and mix until well combined (reserve the remaining reduced stock). Season to taste with salt and freshly ground black pepper.
Once the meat has cooled, chill in the fridge for 1 hour, or until the mixture is firm to the touch.
Cut a 40cm x 30cm/16in x 12in piece of cling film and place it onto a work surface. Shape the mutton mixture into a cylinder shape and place in the middle of the clingfilm. Wrap the clingfilm tightly around the mutton mixture and twist the end several times. Roll the mutton mixture to achieve a smooth cylinder. Chill in the fridge for 2-3 hours.
Fry the butter in a frying pan over a high heat until it becomes dark brown in colour
Add the reserved cooking liquor to the butter, along with the shallots and capers. Season with salt and black pepper.
For the pickled shallots, place the sugar, vinegar and shallots into a bowl and mix until well combined.
Meanwhile for the roast onions, heat the oil in a frying pan and add the onions. Fry until the onions caramelise and are tender. Remove the onions from the pan and drain onto kitchen paper. Season with salt and freshly ground black pepper.
Unwrap the clingfilm from the mutton and carve the mutton into thick slices.
Fry the mutton in a frying pan until brown on both sides then place in the oven to warm through. Add three tablespoons of the reduced stock cooking liquor to coat the mutton. Remove the meat from the pan and roll in the chopped herbs.
To serve, place the roast onions on top of the mutton, drizzle over with the sauce. Serve with the pickled shallots.