In a large frying pan, dry fry the coriander, cumin and fennel seeds for 2-3 min until fragrant and just beginning to pop. Then in a pestle and mortar, grind them to a fine powder.Next, in a food processor or hand blender whizz the onion, tomatoes, chilli, garlic, ginger, turmeric, cinnamon and ½tsp salt to a smooth paste.
Gently heat the oil in the same pan as the spices and add the spice powder and paste along with 3 tbsp water and the curry leaves. Let it sizzle on low heat for 10 mins until you see some oils come from the mix.Now, add the chicken, tomatoes and stock to the pan with the sugar and lemon juice.Let it all simmer for 30 mins or until the meat is cooked.Set aside to cool for 10 mins before stirring through the natural yoghurt. Serve with rice or naan and poppadums.