Mix the lemon juice, garlic, oil and a little salt together in a bowl and stir in the lamb. Cover and marinate in the refrigerator overnight. Place the lamb and marinade in a large pan, add the onion and ginger and cook gently for 5 minutes, stirring occasionally. Add the garam masala, chilli powder, cardamom pods and seasoning. Cook for 2 minutes, stirring continuously. Stir in the tomato puree, tomatoes and stock. Bring to the boil, cover and simmer for 1-1 1/2 hours, stirring occasionally. Carefully stir in the yogurt. Check the seasoning and serve straight away, garnished with chopped coriander.