Put the yoghurt, turmeric and salt and pepper in a bowl and stir to combine. Mix through the chicken, cover and leave in the fridge to marinate for at least 2 hours.
Meanwhile, make the cashew paste. Soak the cashews in 100ml of warm water for half an hour. Put the cashews and their liquid in a blender with the ginger and chillies, blitzing to a smooth paste.
Heat the 2 tea spoons of vegetable oil in a large, lidded saucepan on a medium heat. Add the clove sand cinnamon and let sizzle for a couple of minutes until fragrant. Add the shallots and cook, stirring often, until golden – around 6 minutes.
Add the chicken and fry for 8 minutes until seared all over. Lower the heat, add the sugar, a pinch of salt and 100ml of water. Cover and simmer for 20 minutes, stirring halfway through.
Stir in the cashew paste, simmer for a further 5 minutes, add the cardamom, and take the pot off the heat.
Allow the curry to rest whilst making the temper – heat the 1 tbsp oil in a small frying pan on a medium heat. Add the shallots and cook for five minutes until starting to turn golden. Add the cashews and fry for a further 2 minutes. Add the mustard seeds and curry leaves, cook for 30 seconds. Pour the temper over the curry and serve with rice or chapati.
