Heat the oil in a large saucepan, add the chopped onions and ginger and fry for 3-4 minutes, or until softened but not coloured. Add cumin seeds, ground coriander, ground cumin and chilli powder, if using, and lightly fry until aromatic. Stir in the chopped garlic and fry for one more minute.
Add the chicken pieces, cashew nuts and bay leaf, and allow the chicken to brown slightly over a medium heat. Season with salt and freshly ground black pepper, cover with boiling water, and bring to the boil. Reduce the heat to a simmer and cook gently for 15 minutes.
Stir in the double cream, turn up the heat and allow to bubble for 4-5 minutes, or until the sauce has thickened.
Sprinkle over the chopped fresh coriander and serve with white basmati rice.