Claudia Winkleman's butter chicken

Name: Claudia Winkleman's butter chicken
Cook time: 1 h 30 min
Total time: 1 h 30 min
Cuisine: Indian
Ingredients: FIRST MARINADE; 800g skinless free-range chicken breast; 1 lemon; 5cm piece of ginger; 3 cloves of garlic; 1 teaspoon chilli powder (I used mild); SECOND MARINADE; 1 teaspoon ground coriander; 1 teaspoon ground cumin; 100g Greek set yoghurt; SAUCE; 75g unsalted cashew nuts or 1 heaped tablespoon cashew butter; optional: milk; 1 onion; groundnut oil; 1.5kg ripe tomatoes; 1 tablespoon chilli powder; 2 fresh green chillies; 50g unsalted butter; 1 teaspoon fenugreek powder (kasoori methi); 50g double cream; optional: fresh coriander, to finish; ONION PICKLE; 1 red onion; cider or white wine vinegar; MINT YOGHURT; 1 bunch of fresh mint (30g); 1 teaspoon mango powder; 200g natural yoghurt; CHEAT’S NAAN