Add all the marinade ingredients (excluding the chicken) to a bowl and mix well
Add the diced chicken to the marinade and make sure it is well coated
Cover with cling film and put in the fridge
Leave it to marinade for at least 30mins, but ideally over night
Heat half the oil in a large skillet / pan
Add the pieces of marinated chicken and cook for approx 4-5 minutes until the chicken is cooked through
Take the chicken out of the pan and set aside
In the same pan add remaining oil and the onion and cook for a further two minutes until the onion begins to soften
Add the garlic and ginger and cook for a minute
Add the turmeric, cumin, coriander powder and chilli powder, gently stirring for 20 seconds
Add the chopped tomato / passata
Add salt / sugar to taste
Cook on a low heat so the sauce is just simmering for approx 15-20mins until the sauce thickens
Add the chicken back to the sauce and add the cream and gently stir to mix
Add the garam masala and cook for a further 10 minutes or until the the chicken is cooked through - add water if necessary
Garnish with the chopped coriander and serve