Cut the chicken so that the legs are separated from the thighs, cut each breast in two lengthwise.
Mix together in a bowl the turmeric, fennel, coriander and chili powder with 3 tbsp water to make a paste.
Heat the oil over medium heat and fry the onions, ginger and garlic, till the onions are brown, 5 minutes.
Turn the heat to low and fry the spice paste stir and cook for 5 minutes To the bowl in which the spices were mixed add 3 tbsp water, stir to remove all traces of the spices and add the water to the pan. Stir and cook 3 minutes.
Turn the heat to medium and add the chicken, stir and fry for 4 minutes, till the chicken changes colour.
Add 1 tsp of the salt and the water, bring to the boil, cover with a lid, reduce the heat and simmer for 20 minutes.
Melt the butter in a separate pan and add the garlic, curry leaves, cumin, fennel and red chillies. Stir and add the spinach and 1/2 tsp salt. Fry for 5 minutes.
Add the spinach to the chicken mix well, cover the pan and cook for 20 minutes.
Mix in the yogurt and garam masala stir well to blend the yogurt with the chicken and spinach . Cook uncovered 6 minutes, stirring frequently.