Purée ginger, garlic, chillies. Stir in yoghurt and cumin. Pour over lamb and leave to marinate for an hour or overnight.
Blanch spinach in little salted water until wilted. Process to a puree.
Heat oil in a heavy-based pot or pan. Add bay leaf, cardamom, and cloves and heat until the bay leaf is getting crisp, then add the onions. Fry for 15 minutes over low-med heat.
Add coriander and cumin and cook for 1-2 more minutes, adding a splash of water if you need to.
Add meat and marinade to the spices and cook for 10 minutes until yoghurt is absorbed. Add tomatoes and bring to a simmer for 3-5 minutes. Add water and salt, cover and simmer on low for 45 minutes to an hour until the meat is well-tender.
Add puréed spinach, mix well and cook uncovered for 5 minutes or until thickened. Taste for extra salt.
Serve with rice and/or roti and add a squeeze of fresh lemon juice just before serving.
