Mix all the ingredients for the glaze in a bowl and set aside.

Put the lamb in a large, high-sided roasting dish lined with greaseproof paper.

In a small bowl, combine the mixed spice, cumin, sugar, oil, one and a half teaspoons of salt and a quarter-teaspoon of freshly ground black pepper, then rub this evenly all over the lamb. Leave to marinate at room temperature for an hour, or ideally put it in the fridge overnight (if it’s been in the fridge, take it out an hour before you want to cook, so it comes back to room temperature).

Heat the oven to 240C (220C fan)/475F/gas 9.

Put all the remaining ingredients for the lamb in the tray around the meat, then cover tightly with foil and roast for 15 minutes.

Turn down the oven to 180C (160C fan)/350F/gas 4 and leave the lamb to cook for four hours, until the meat is tender and falling apart easily.

Take the roasting dish out of the oven, lift off the foil, then brush three-quarters of the glaze all over the lamb. Return the dish to the oven and roast uncovered for another 30 minutes, until the meat develops a nice crust.

Take out of the oven again, brush all over with the remaining glaze, then cover lightly with foil and leave to rest for 10 minutes before serving.