Take a small bowl and add the crushed garlic, a good pinch of salt, the butter, spices, olive oil and mix until smooth.
Prick the lamb all over with a sharp knife and rub the spice paste all over the lamb, massaging it in as you go. Place in a shallow dish, cover and refrigerate over night.
Preheat the oven to 200C / 180C fan / Gas 6 / Roasting & Simmering Oven AGA
Take the lamb out of the fridge and allow it to come to room temperature (45 mins approx).
Place in a small roasting tray and add 100ml of water to the tray. Cover with foil and put into the hot oven. As soon as you have put the lamb in reduce the temperature to 180C / 160C fan / Gas 4 (see below for AGA cooking) and cook for 3-3 1/2 hours until tender and the meat can be pulled apart with a fork.
Remove the lamb from the oven, take out of the roasting tin and leave to rest for around 20 minutes.
While the lamb is resting pour the remaining juices into a small pan, bring to a boil, reduce to a simmer for 5-10 minutes to reduce by half.
Using two forks, shred the lamb and transfer to a serving plate. Season and pour the reduced juices over the lamb, mix together.
Scatter over the herbs, crumble the feta and sprinkle over the pomegranate seeds and serve immediately.