Madhur Jaffrey's Chicken Tikka Masala

Ingredients:
For chicken:                                                          For masala:
675g boneless, skinless chicken thighs                    4tbsp olive oil
           or breasts, cut in to 2cm chunks                  140g onions, halved and finely sliced
1 tsp salt                                                               1 tbsp peeled, finely grated ginger
3 tbsp lemon juice                                                 5-6 garlic cloves, crushed
1tbsp peeled, finely grated root ginger                   1 tbsp ground coriander
2 garlic cloves, finely grated or crushed                  1/2 tsp turmeric
1 tsp ground cumin                                                 1/4 tsp chilli powder
1 tsp paprika                                                          2 tsp paprika
1/2 tsp chilli powder                                              4 tbsp yoghurt
6 tbsp whipping cream (or plain yoghurt)                 2 medium tomatoes, peeled and finely chopped
1/2 tsp garam masala                                              350ml chicken stock
3 tbsp olive oil                                                        1/4 tsp salt
                                                                              1/4 tsp garam masala
                                                                              4 tbsp chopped coriander leaves

Instructions:
1. Marinate the chicken tikka. Put the chicken in a bowl and rub the salt and lemon juice. Prod the chicken pieces gently with the tip of a knife, rub the seasonings in again and then set aside of 20 minutes.
2. Add the ginger, garlic, cumin, paprika, chilli powder, cream and garam masala. Mix well, cover and refridgerate for 6-8 hours (or longer)
3. Make the masala: pour the 4 tbsp of oil into a large, non-stick, lidded pan and set over a medium-high heat. Put in the onions, stir and fry until brown (6-7 minutes). Add the ginger and garlic and continue to fry, stirring for a minute more. 
4. Add the ground coriander, turmeric, chilli powder and paprika. Stir for 10 seconds, then add a tablespoon of the yoghurt. Stir and fry until absorbed. Add the remaining yoghurt in this way, a tablespoon at a time. 
5. Put in the tomatoes. Fry for 3-4 minutes or until pulpy. Add the stock and salt, and bring to a simmer. Cover, reduce the heat to low, simmer gently for 15-20 minutes. The sauce should turn thick. 
6. Stir in the garam masala and coriander leaves. Taste for balance of seasoning and add more salt if necessary. 
7. Shortly before you eat, preheat the grill to its highest setting. THread the chicken on to two or four skewers. Brush with 3 tbsp of oil and balance on the rim of a shallow baking tray, so the meat is suspended. Place under the grill for six minutes on each side. 
8. When the tikkas are cooked, reheat the sauce and fold in the chicken. Serve immediately.
   
Taken from Madhur Jaffrey's Curry Nation