To make the lamb shoulder, gently warm 2.5 litres/4¼ pints water in a saucepan large enough to hold the lamb. Add the saffron and then the other spices, the bay, the ginger and garlic and salt. Bring to a simmer then gently lower the lamb into the pot, top with half the onions and cover with a lid. Simmer gently for 5–6 hours, until the meat is falling off the bone, keep an eye on the liquid level and add a little more each time it has reduced by half.
Preheat the oven to 200C/180C Fan/Gas 6 and place the butter and oil in a roasting tin.
Remove the lamb from the saucepan and transfer to the roasting tin. Baste the lamb all over with the butter and oil then roast for 30–40 minutes, until the lamb is crisp.
Add the remaining onions to the lamb poaching liquid, bring to the boil then simmer for about 30 minutes, to make a sauce. Remove from the heat.
To serve, toast the peanuts in a dry pan over a medium heat for 5 minutes.
Remove the lamb from the oven, pull the meat from the bone and pile it onto plates to serve with the poaching liquid sauce. Scatter the nuts, spring onions and herbs on top.
