Indian spice box chicken.  - 25g fat green mild chillies.  - 1 1/2 large garlic cloves.  - 2 1/2 piece of fresh root ginger.  - bunch of fresh coriander.  - 100g carton of full-fat Greek yogurt.  - 1 medium onion.  - 4 medium bone-in chicken thighs  - 1 tbsp groundnut or corn oil.  - 1 tsp fennel seeds.  - 1/2 tsp cumin seeds.  - good knob of butter.  - Chilli-ginger garnish.