Wash the basmati rice until the water runs mostly clear, then soak it in enough water to cover for 20 minutes.

Slice the onions, cube the potatoes, and chop the fresh coriander if using.

Blend the tomatoes with the small green chillies into a smooth paste.

Heat 1 1/2 cups cooking oil in the large pot over medium heat, then fry the sliced onions until deeply golden brown.

Remove half of the fried onions with a slotted spoon and reserve them for the final garnish.

Add the chicken boti and ginger-garlic paste to the pot, then sauté for 5 minutes until the meat is lightly browned.

Add the black peppercorns, cumin seeds, green cardamom pods, cinnamon stick, bay leaf, whole black pepper, and star anise.

Stir in the red chilli powder and turmeric powder, then cook the spices for 1 minute.

Pour the tomato-chilli paste into the pot, then cook it for 8 minutes until it darkens and the oil begins to separate.

Add 2 cups water and simmer covered until the chicken is tender, about 20 minutes.

Uncover the pot and cook the gravy over medium-high heat until excess liquid reduces and oil rises to the surface.

Add the cubed potatoes, medium green chillies, and salt, then stir until evenly coated in the masala.

Pour in the remaining 4 cups water and bring the liquid to a full boil.

Drain the soaked basmati rice and add it to the boiling gravy, then gently stir once to distribute the rice.

Cover the pot and cook over medium heat until the water is nearly absorbed, about 10 to 15 minutes.

Scatter the reserved fried onions and fresh coriander over the rice, then cover the pot tightly.

Steam the akni on the lowest heat for 15 minutes, then rest it covered for 5 minutes before fluffing and serving.