• Preheat the oven to 170C (340F)
• Score small slits into the lamb fat and stuff with large slices of garlic and rosemary sprigs.
• Layer the anchovy fillets on top of the lamb. Keep the oil for step 5.
• Slice the onions into rings and layer on a baking tray along with any leftover garlic and rosemary.
• Sit the lamb shoulder on top of the onions, drizzle with the anchovy oil and season well with salt & pepper.
• Add the water to the bottom of the baking tray.
• Cover the lamb and baking tray entirely in tin foil so there are no gaps.
• Roast in the oven for 4 hours.
• After 4 hours, remove tin foil and cook for a further 30 minutes.
• Rest for 10-15 minutes before serving.

To make the Gravy

• Collect the juices that run off the lamb and any in the bottom of the baking tray.
• Skim off as much of the fat as possible.
• Blend the juices with the roasted onions using a stick blender.
• Reduce on the stove on a low heat to thicken further if necessary.