Heat 2 tablespoons of oil in a large pan.
Fry the potatoes in the oil until they become brown. Set aside on a plate.
Add the remaining 2 tablespoons of oil to the pan. Fry the onion, garlic, and ginger until the onion is golden. Add the chili powder, pepper, turmeric, cumin, salt, and tomatoes. Cook for 5 minutes, stirring constantly.
Stir in the yogurt, mint, ground cardamom, and cinnamon stick. Cover and cook over low heat, stirring occasionally, until the tomatoes are reduced to a purée.
Tip: add a little water if the mixture becomes too dry and starts sticking to the pan.
Add the chicken and mix well. Cover and cook on very low heat for 35 minutes. After 35 minutes, there should be very little sauce left.
Rinse the rice under water to wash it.
Heat the oil in a large pot. Fry the onion in the oil until golden.
Add the saffron, cardamom pods, cloves, cinnamon stick, ground ginger, and the rice.
Add the chicken broth and salt to the rice. Stir continuously.
Add the chicken and potato mixture to the rice and bring to a boil.
Then add the cashews.
Reduce the heat to low and cook for 20 minutes with the lid on.
Serve the biryani in a serving dish.