Preheat the oven to 350°F/180°C/gas 4.
For the spice paste: Combine the saffron with the 2 teaspoons of boiling water, and leave to soak.
Heat a small skillet over high heat, then dry-roast the fennel seeds, star anise, cardamom pods, cumin seeds, cinnamon and Sichuan peppercorns for about 2 minutes, or until fragrant. When the spices have cooled, remove the seeds from the cardamom pods, then place them with the dry-roasted seeds in an electric grinder, and grind until the mixture is finely ground. Set aside.
In a suitable container, grind the chillies, garlic, ginger, cilantro stems and roots, turmeric and galangal with an electric stick-blender until you have a coarse paste. Lightly crush the peppercorns with a mortar and pestle or a heavy rolling pin, and add to the chilli/garlic mixture with the sea salt. Add the shallots, saffron strands with their soaking water, paprika, the reserved ground spices and the olive oil to this paste, and mix well to combine.
Heat a heavy-based, medium-sized frying pan over high heat, then add the paste and cook, stirring regularly, for about 5 minutes or until fragrant. Reduce heat and simmer gently, stirring occasionally, for 15 minutes. Add the palm sugar and fish sauce, increase the heat and simmer, stirring occasionally, for a further 2 minutes, or until mixture is slightly caramelised. Remove from stove and set aside.
Brush a roasting tin with some olive oil and heat on the stove top. Season the lamb shanks with salt and white pepper, then add to the roasting pan and seal until lightly browned on all sides.
Drain off any excess oil and increase the heat. Drizzle the prepared spice paste over lamb, and toss and stir the contents of the tin to ensure the shanks are well coated, and to seal in flavours. Add the tomatoes, potatoes, carrots, onions, dates, apricots and bay leaves, and stir to combine.
Remove the tin from the stove, pour over stock and cover with foil. Bake for 45 minutes, then remove foil and bake for a further 1 hour, or until lamb is very tender and well browned.
When the meat is done, drizzle with lime juice and fish sauce before serving.
Serve with cous cous, rice or crusty bread and a large green salad.