1. Pre-heat the oven to 325°F/Gas Mark 3.
  2. Melt the butter in a casserole dish or a large saucepan over a medium heat. Season the chicken pieces with sea salt and freshly ground black pepper. Working in batches, brown the chicken pieces, until they are golden brown on all sides. This should take 5 minutes per batch. Then transfer to a plate.
  3. Add the onions to the pot that you cooked the chicken in (add more butter if needed). Cook, stirring often, until onions are soft and golden brown.
  4. Stir in the garlic, ginger, coriander, cumin, turmeric, and cayenne, stirring constantly, until the spices are fragrant. Then stir in the chickpeas and the chicken broth. Return the chicken pieces and their juices to the pot. Bring to a simmer, cover the pot, transfer to the oven and cook for 45-55 minutes or until the chicken is tender.
  5. Remove the pot from the oven and place over a low heat, then stir in the spinach which should only take one minute to wilt.
  6. Transfer the curry to a large deep platter, serve with a dollop of Greek yoghurt and flat leaf parsley.