- Heat the oil and butter in a non-stick saucepan. Add the onion, season lightly and fry until soft and then until golden at the edges.
- Meanwhile, blend the tomatoes and cashews until smooth.
- Add garlic and chillies (if using) to the onions and cook gently for 30-40 seconds, or until the garlic smells cooked.
- Add the blended tomatoes, turn up the heat and cook until thick and darkened considerably, around 10-12 minutes. Once the masala is cooked, it will release oil droplets back into the pan.
- Add the chicken, the Butter Chicken paste and 150ml water, bring to a simmer and cook until chicken is cooked through, around 8 minutes. Taste, add extra tomato puree if it isn’t tomatoey enough. Add extra boiling water if it is too thick. Stir in the double cream, taste and adjust seasoning to taste and serve.
If you are grilling the chicken
Put the grill on 275°C before you start. Stir together the paste and the yoghurt and season lightly. Add in the chicken (ideally at room temp.) and coat well. Place on an oiled baking tray and grill for 8 minutes on the upper middle shelf, or until lightly charred in places. Tear or cut into large pieces and add to the curry (along with any juices in the pan) - as above, but with only half the water (75ml) and only cook for 3-4 minutes, or until cooked through. Finish as above.