To make the marinade, peel and roughly slice the ginger, peel the garlic cloves, then place in a dry frying pan on a medium heat with the fennel seeds and cardamom pods. Leave for 1 minute to wake up all those lovely flavours, then tip into a pestle and mortar. Pound to a rough paste with the chilli powder and a pinch of sea salt. Transfer to a large sealable bag, finely grate in the lemon zest, squeeze in the juice and add the yoghurt. Remove the chicken skin, then place in the bag, seal and massage to coat. Marinate in the fridge for at least 1 hour, preferably overnight. Preheat the oven to 190ºC/375ºF/gas 5. Peel and finely chop the onion. Peel the potatoes, then chop into rough chunks with the tomatoes. Finely chop the coriander stalks (reserving the leaves). Place a large, wide ovenproof pan on a medium heat with 4 tablespoons of oil, the cinnamon, cloves, cumin seeds and bay. Add the chicken in a single layer with its marinade and cook for 5 minutes on one side, or until a lovely golden crust develops. Stir in the ground spices, then add the onion, potatoes, tomatoes and coriander stalks. Turn the chicken and cook for a further 5 to 10 minutes, or until browned all over. Pour over 350ml of cold water, then bring to the boil. Transfer to the oven for 50 minutes to 1 hour, or until the chicken is tender, stirring occasionally. Pick out and discard the cinnamon and any visible cardamom pods, then finely slice and sprinkle over the chilli (if using). Tear over the coriander leaves and serve. Great with a dollop of yoghurt, coconut rice, naan breads and a fresh green salad.