In a pestle and mortar, add 3 fresh green finger chillies (seeds & pith removed for milder heat, left in for more heat), thinly sliced and pinch sea salt. Pound to a paste (be careful and look the other way to avoid any chilli splashback!). Add 1 teaspoon vegetable oil, mix and set aside.
Heat 2 teaspoons vegetable oil in a frying pan or curry pan over medium heat. Add 1 small onion, finely chopped, 1/2 red pepper, finely chopped and 1/2 green pepper, finely chopped and stir-fry for 2 minutes. Add 80 millillitres curry broth, 1 teaspoon garlic ginger paste, 1 teaspoon tomato puree, 1/4 teaspoon mild red chilli powder, 1/4 teaspoon beetroot powder, 1 teaspoon dried fenugreek leaves (methi) and 1 small handful fresh coriander leaves, finely chopped. Bring to the boil, then add 8-9 pieces slow cooked lamb for Indian curry dishes and another 80 millilitres curry broth. Mix well and simmer for 2 minutes.
Add the remaining 80 millilitres curry broth, 50 millilitres single cream, 1 teaspoon ground almonds, 1 teaspoon cashew butter, 1 teaspoon salted butter and 1/4 teaspoon garlic powder. Mix well and simmer for 2 minutes until the South Indian garlic chilli curry sauce is medium thick and bubbling hot.
Transfer the South Indian garlic chilli lamb curry to a serving bowl. Garnish with pinch garam masala, 1 teaspoon single cream, small pinch fresh coriander leaves, finely chopped, 1 fresh green finger chilli, sliced and 1/2 spring onion, sliced. Serve with your favourite Indian rice and breads.