1. Heat the oil in a saucepan then add the chopped onions and cook until browned; the darker the onion, the deeper the flavour. Remove from pan and set aside.
2. Meanwhile, blend together the tomatoes, the curry paste, paprika, garam masala, salt and yogurt to a smooth paste.
3. Once you have removed the onions place the pan back onto the heat. When hot add the chicken to the pan and seal the outside. Add the tomato-yogurt paste and bring to the boil, stirring frequently. Then reduce the heat, cover and cook for 15 -20 minutes, or until the chicken is tender. Mix in the sliced onions 10 minutes into the cooking process and give the chicken a stir making sure it does not dry out. Ideally, the dish should cook in its own sauce but, if necessary, add a splash of water.
4. By the time the chicken is tender, the sauce should have reduced to a creamy consistency with a tangle of sweet, sliced onions. If it is too dry, add a splash of water.
5. Season and add lemon juice to taste. Stir in the chopped coriander and serve with Paratha, Chapati or Naan bread.

For lamb or mutton dopiaza increase the cooking time to 45-50 minutes and add the browned onions 30 minutes before the end of the cooking time.