Mix Curry Marinade ingredients in a large bowl. Add chicken, tossing to coat well. Marinade 30 minutes to overnight, covered. If chicken is refrigerated overnight, bring to room temperature before cooking.
Bring 8 cups water with salt to the boil. Add rice, bring back to the boil then cook for 5 minutes, or until rice is just cooked, but firm in the middle. This is par-boiling the rice. Drain and set aside.
Heat the 1/2 cup oil in a Dutch oven (or large deep skillet) over medium-high heat. Shallow fry sliced onion in 2 batches for 4 to 5 minutes, or until a deep golden brown. Transfer to paper towel lined plate to drain. Season with salt. Repeat with remaining onions. Transfer remaining oil to a large Dutch oven if using skillet.
Grind saffron and place in a small bowl. Mix with 2 tablespoons warm water and the 2 tablespoons melted ghee (or butter). Set aside to bloom.
Chop both cilantro and mint leaves and place in bowl. Set aside.
Heat Dutch oven over medium heat with oil from onions and add 1 tablespoon oil. Transfer chicken and marinade to pan, cover and cook for 5 minutes. Remove lid. Turn chicken and cook for another 5 minutes.
Remove Dutch oven from heat and place on other burner without a flame.
Turn chicken skin-side down and scatter half the crispy onions on top, then the cilantro/mint leaves, reserving 2 tablespoons for serving.
Top with all the rice and gently pat down and flatten top. Drizzle saffron water ghee mixture over the rice. Cover and cook on low for 30 minutes. Remove from stove, rest with lid on for 10 minutes.
Discard any whole spices and bay leaves that you can find if preferred. Carefully scoop deep into pot to get chicken and mixed rice and place into large serving bowl or platter. Garnish with remaining crispy onions and reserved 2 tablespoons cilantro and mint leaves.