In the jar of a blender, combine yogurt, garlic, jalapeño peppers, cumin seeds, and salt and blitz until smooth. Pour over chicken and set aside.

Heat half of the oil in a large vessel over medium heat. Add half of the onions and cook until lightly browned. Add chicken and yogurt mixture, and cook until the chicken is mostly cooked through, and the oil starts to separate from the curry, about 15 to 20 minutes. Remove from heat and set aside.

Heat remaining oil in a small pan over medium high heat. Add remaining onions and diced potatoes, and cook, stirring often, until golden brown. Transfer the contents of this pan to the cooked chicken.

Bring the vessel containing the chicken back to the stove, and add tomatoes, lemon juice, cilantro, cardamoms, cloves, cinnamon, cumin, and black peppercorns. Add drained rice and 3¼ cups water and bring to a boil. Cover, reduce heat to medium low, and cook for 15 minutes. Remove from heat, and allow the rice to sit undisturbed (do not remove lid) for an additional 15 minutes.