To make the sauce, melt ghee in a wide, heavy-based saucepan over moderate heat and fry onion until softened. Add turmeric and fry until fragrant, then stir in green masala paste and spiced tomato chilli pickle. Cook for a few minutes until mixture starts to bubble, then stir in tomato purée and cook for another minute. Add stock and cook gently for 25 minutes, or until