Empty the can of chopped tomatoes into a blender and pulse / blend until smooth, about half a minute
Heat the butter, add the onion and fry until tender.
Stir in the garlic and ginger and cook briefly before adding the chilli powder, turmeric, cumin and garam masala
Stir for a minute before adding the blended and smooth Tomato and brown sugar Season to taste, cover, reduce heat and simmer for 10 minutes.
Add the yoghurt and allow to cook for about 2 minutes then add the chicken, covering it with the sauce. and simmer for a further 10 -15 minutes until the chicken is cooked through and the sauce slightly reduced and thickened.
Reduce the heat to low when the chicken has cooked and allow to sit in the sauce for 10 more minutes to allow the flavours to be absorbed well into the chicken.
Garnish with chopped coriander leaves and serve with naan or basmati rice.