To make the marinade, peel and roughly slice the ginger, break up and peel the garlic cloves, then add to a dry frying pan over a medium heat, along with the fennel seeds. Heat for a minute to wake up the flavours, then transfer to a pestle and mortar with the chilli powder and a pinch of sea salt, and pound into a rough paste. Tip into a large bowl with the yoghurt, lemon zest and juice, and the chicken thighs. Stir to coat evenly, then cover and place in the fridge to marinate for at least 1 hour, but preferably overnight.
Peel and finely dice the onions. Chop the tomatoes. Pick the coriander leaves and set aside, then finely chop the stalks. Heat 4 tbsp of oil in a large pan over a medium heat, then add the cinnamon, cloves, cumin seeds and bay and let cook for five minutes. Do not burn them! Add the chicken in a single layer and cook for 5 minutes on one side, or until a golden crust develops. Stir in the ground spices, then add the onion, tomatoes and coriander stalks. Turn the chicken over and cook for a further 5 -10 minutes, until browned all over. Pour over 350ml of cold water or chicken stock, then bring to the boil.
Turn down to a medium heat and cook for about 30 minutes uncovered, or until the chicken is cooked through and tender, stirring occasionally. Pick out and discard the cinnamon and divide between your plates. If using the chilli, finely slice it and sprinkle over the plates, tearing the coriander leaves on top. Serve with a dollop of yoghurt, plain rice and dal if you like.