Combine all ingredients except chicken in a bowl and mix. Add chicken and turn well to coat.

Cover with cling wrap and leave in fridge to marinate overnight (3 hours minimum).

Heat 1 tablespoon oil in a non stick pan over high heat until smoking. Add half the chicken and spread out. Leave for 2 minutes or until charred. Turn each piece and cook the other side until charred. Remove into bowl.

Scrape out charred bits left in pan and discard. Add more oil if required and cook remaining chicken.

Wipe skillet with paper towels. Turn heat down to medium high.

Add oil and butter. When butter is melted, add onions, ginger and salt.

Cook, stirring constantly until the ginger is starting to turn golden and the onions smell sweet, about 5-7 minutes.

Reduce the heat to medium. Add the garlic and paprika, and cook for 2 minutes.

Add the Curry Sauce Spices, and cook a further 2 minutes, stirring.

Add tomato passata and water, and mix. Bring to a simmer, then cover and reduce heat to low.

Simmer for 15 minutes, stirring occasionally.

Pour curry into a bowl, then use a stick blender to puree until smooth.

Return sauce to skillet. Add cream, sugar and butter. Stir to melt the butter.

Add chicken, stir. Simmer for a few minutes until the chicken is cooked through.

Optional: Sprinkle with a pinch of extra garam masala at the end.

Serve over basmati rice, sprinkled with coriander/cilantro if desired.