Place all the chicken marinade ingredients into a bowl and mix. Allow to sit in fridge for at least 1 hour. For best results allow it to sit overnight.
Wash the rice and parboil in salt seasoned water.
While the rice is cooking in a separate pan place the oil medium heat. When hot add the chicken thighs and partially cook until the marinade forms a golden crust on the chicken. Don't cook until completion as the chicken will continue to cook through when cooking the biryani.
While the chicken and rice is cooking roughly chop the onions, place in a blender and blend to form onion paste.
Remove the chicken from the pan. There should still be oil. Increase to high heat and when hot add the blended onions. It is important that when the blended onions hit the pot there is a rapid sizzling sound. (See note 1)
The onion paste needs to keep frying on high heat until the oil and gravy move as one and the raw onion smell is gone. (See note 2)
When the raw smell is gone reduce to medium heat, add the spices and salt and allow to fry to release the aromas then add raising and cashews.
At this stage the rice should be par boiled. Strain the rice and rinse through with cold water to slow down the cooking process.
Aim to use a pot size that will allow you to layer rice and biryani paste about 2 times.
To layer the biryani place all the chicken thighs at the bottom of the pot. Then place in layer in the following order:
The final layer should finish with plain rice.
For presentation prepare the imitation saffron by mixing in a bit of water and drizzling on the top.
Securely close the lid of the clay pot and place in oven set to 150C for 60 mins.
Remove from oven and allow to rest for at least 30 minutes. Note that the oil will settle to the bottom of the pot. It is best to transfer the biryani rice and lightly mix the layers after resting, this way you can serve the rice and get to the tender chicken on the bottom of the pot easily.
This dish is traditionally served with pepper water, belachan and pickle salad but, if you want something quick to balance it with some freshness, a quick lettuce tomato and cucumber salad with balsamic dressing will suffice.
Note 1: The onion paste needs to literally fry, like shallow fry in the oil. A failure to ensure high heat when the onion hits the pan means that the onion gravy will struggle to become sweet and caramelized.
Note 2: The onion paste needs to be suspended and somewhat swimming in the oil. If the ratio of oil to onion is a bit off feel free to add in more oil to the pot to encourage full caramelization.