This is an amazing curry and you can beef or chicken (used in the photo) instead of lamb for this lamb and spinach karahi. Heat the oil in a karahi (or wok), add onions and cook gently for 20-30 mins until soft and light brown. Put tomatoes, water, ginger and garlic into a whizzer and whizz until smooth. Remove the fried onions with a slotted spoon, add them to paste and whizz again.
Return puree to the pan and add lamb and salt. Simmer for 30 mins, by which time the lamb should be half cooked and the sauce well reduced. Stir in the turmeric, chilli powder, cumin, paprika and coriander and continue to cook for 30-45 mins (shoulder) or 45mins-1hr (leg) until lamb is tender, adding water now and then if sauce starts to stick.
Meanwhile, put 175g spinach into a large pan and wilt. Cook for 1 min, then transfer to rinsed out whizzer and blend to a smooth puree. Set aside. Rinse out the whizzer and add the green chillies and 2-3 tbsp water and blend until smooth. Set aside.
When the lamb is cooked stir in the spinach puree and the remaining leaf spinach and cook for 2 mins. Now taste the curry and add as much green chilli puree as you wish. Simmer for 2 mins then serve.
Garnish with the cumin and pepper.