2 large white sweet potatoes, peeled and cut into chunks
2 large potatoes, peeled and cut into chunks
2 tbsp olive oil
10 garlic cloves, peeled
For the smoked chilli tamarind sauce
200ml/7fl oz high-quality beef or lamb stock
400g/14oz dark brown sugar
130g/4½oz tamarind concentrate
100ml/3½fl oz pomegranate molasses
20g/¾oz smoked chipotle chilli paste
For the mango salad
1 mango, peeled and sliced
2 tbsp basil leaves
2 tbsp parsley leaves
2 tbsp coriander leaves
2 tbsp mint leaves
1 lemon, juice only
2 tbsp rapeseed oil
Score small incisions into the lamb with a sharp knife. Mix together the spices and the oil and rub into the skin. Cover and leave to marinate in the fridge overnight, or for at least an hour.
For the sweet potatoes, preheat the oven to 200C/180C Fan/Gas 6.
Boil the potatoes in salted water for 5 minutes, drain and leave to air-dry.
Pour the oil into a deep baking tray and put in the oven for 5 minutes. Remove the tray from the oven, then add the potatoes and garlic. Stir well and return the tray to the oven for 35¬–40 minutes.
For the sauce, put all the ingredients into a saucepan placed over a medium heat. Cook until the sugar is dissolved and the sauce has thickened until it can coat the back of a spoon.
When you are ready to cook the lamb, heat a griddle pan over a high heat. Griddle the lamb for 4–5 minutes until caramelised, turning halfway though. Brush the lamb with the chilli and tamarind sauce, reduce the heat and leave the lamb to cook for another 8 minutes. Turn over and cook for a further 8 minutes. Transfer to a board and leave to rest for 15 minutes before carving.
Meanwhile, to make the mango salad, place the mango and herbs into a large bowl. Mix the lemon and oil together in a small jar and drizzle over the salad.
Slice the lamb and place onto a platter. Scatter the potatoes around the lamb and drizzle with the sauce. Serve alongside the mango salad.