Old Delhi-style butter chicken

Name: Old Delhi-style butter chicken
Prep time: 50 min
Cook time: 1 h
Total time: 1 h 50 min
Cuisine: Indian
Ingredients: 800g boneless and skinless chickenthighs, cut into bite-sized pieces; corianderleaves, finely sliced red onion, sliced green or red chilli, naan bread or basmati rice, and chutney, to serve; 120g Greek yogurt; thumb-sized piece ginger,grated; 4-5 garlic cloves,crushed; 1 tbsp vegetable oil; 1 lemon,juiced; 3 tsp mild chilli powder; 1 tsp ground cumin; ½ tsp garam masala; ½ tsp turmeric; 1kg ripe vine or plum tomatoes; thumb-sized piece ginger,peeled, half grated and half finely chopped; 4 garlic cloves,crushed; 4 green cardamom pods; 2 cloves; 1 bay leaf; 1-2 tsp chilli powder; 80g butter,diced; 2 green chillies,cut lengthways; 75ml single cream,plus a drizzle to serve; 5-6 dried fenugreekleaves, crushed between your fingers (optional); 1 tsp garam masala; 1 tbsp sugar; 3 tbsp ghee (see below) or butter; 2 tsp black mustard seeds; 1 dried whole Kashmiri chilli; 6-8 dried curry leaves