Blend the garlic, ginger, vegetable oil and 4 tablespoons water to a purée in a food processor.
Heat the ghee in a heavy-based saucepan over a medium heat. Add the garlic and ginger purée and fry for 1-2 minutes, then add the cardamom pods, bay leaves and cinnamon sticks.
Add the onions and fry for 4-5 minutes, or until slightly browned.
Add the salt and 500ml/17fl oz water. Bring the mixture to the boil, then reduce the heat until it is simmering. Half-cover the pan with the lid and simmer for 12-15 minutes, or until the water has nearly evaporated.
Stir the onion mixture, then add another 500ml/17fl oz water. Simmer, half-covered, as before, for 12-15 minutes.
Repeat this process 5 more times - this draws all of the natural sweetness from the onions and helps break them down to sweet and silky sauce.
Add the chicken pieces and cover with 250ml/9fl oz water. Bring the water to the boil, then reduce the temperature until it is simmering. Cover the pan with the lid and cook the chicken for 15-20 minutes, or until cooked through. (The chicken is cooked through if the juices run clear when the thickest part of the chicken is pierced with a skewer and no trace of pink remains.)
Serve in bowls with steamed pilau rice.