THE DAY BEFORE
Mix the lemon juice and zest, grated ginger, crushed garlic, chilli powder and salt together in a large bowl and add the chicken. Use your hands to coat well. Set aside in fridge for 1 hour.
Mix the yoghurt with the ground coriander and cumin and pour over the chicken. Mix well and leave overnight in the fridge, covered.
Soak the cashews overnight in 70ml water. When you’re ready to make your sauce, drain the liquid then grind the cashews to a paste in a pestle and mortar (or use a blender), adding a splash of milk to loosen if needed. Set aside.
ON THE DAY
To make your sauce, place a large pan on a medium-high heat with 2 tablespoons of vegetable oil. Add the chopped onion and cook for 5 minutes, until softened but not coloured.
Add the tinned tomatoes to the pan with a good pinch of salt, cumin, cardamom pods and cloves. Cook for 15 minutes, breaking them up with the back of a wooden spoon, until soft and cooked right down. Remove from the heat and blend the mixture with a stick blender and finally press through a course sieve set over a clean bowl to make a smooth puree.
Return the puree to the pan and slowly heat. Add the chilli powder and fenugreek.
Fry the halved green chillies on a medium-high heat with 1 tablespoon of the butter for 2 to 3 minutes, until golden and aromatic, then pour into the tomato sauce. Slowly incorporate the rest of the butter, stirring. Finally, add your cashew nut paste and set sauce aside.
Set your BBQ up for grilling.
Thread your chicken onto skewers and cook on the barbecue for 15-18 minutes, turning after 10 minutes or so. The chicken should be a little blackened in parts but still slightly pink in the middle.
Heat your sauce to a gentle simmer and add chopped ginger and cream. Carefully remove the chicken from the skewers and place into the sauce, simmering for a further 5-10 minutes, or until the chicken is completely cooked through.