Cut the chicken into bite size chunks and marinate in the fridge coated in the yogurt for at least 1 – 4 hours.
In a pestle and mortar crush the cardamom pods and remove their skins, just leaving the crushed seeds. Add the cumin, coriander, turmeric, chilli powder and clove ends to the cardamom seeds.
Dry fry the cashew nuts in a frying pan until golden brown but not burnt.
Gently heat the oil in a medium sized saucepan. Add the onions and the garlic and ginger paste. Sauté for about 3 minutes.
Stir in the spices from the pestle and mortar. Cook, stirring for 30 seconds.
Add the corn flour mixture and stir for about 30 seconds. Then add the cold water and mix, stirring together well.
Bring the mixture to the boil, turn the heat down to simmer for 10 minutes stirring from time to time. Then remove saucepan from the heat.
Once the mixture has cooled enough to handle blitz it in a food processor / blender until it is of a sauce consistency.
Pour the sauce back into the pan, bring it up to a simmer again and stir in the sugar and tablespoon of yogurt.
Season to taste with the salt and pepper. Add extra sugar if necessary.
Add the marinated chicken and mix thoroughly into the sauce.
Cook the curry for 15 – 20 minutes checking to see if the chicken is thoroughly cooked through by cutting one of the pieces in half. Once cooked turn off the heat. Stir in the toasted cashew nuts to warm them through.
Serve garnished with the fresh coriander on a bed of basmati rice.