Place the basmati rice in a bowl of cold water and soak for 30 minutes, then drain and rinse under cold water until it runs clear; set aside.
Preheat the oven to 160°C (fan) while the rice soaks.
Heat 3 Tbsp olive oil in a large ovenproof casserole over medium heat. Add the chicken pieces and sauté until golden brown on all sides, then remove and set aside.
Reduce the heat to low and add the butter. Stir in the chopped onion, grated carrot, cinnamon quill, star anise and thyme stalks and cook, covered, until the onion is translucent, about 5 minutes.
Add the ground cumin, turmeric, smoked paprika, a pinch of chilli flakes and crushed garlic; cook for about 1 minute until fragrant.
Deglaze the pan with the 1/2 cup fresh orange juice, scraping up any browned bits, then stir in the orange marmalade and cook until most of the liquid has evaporated.
Add the rinsed, drained rice and toss to coat in the flavored butter and oil for about 1 minute.
Pour in the hot chicken stock and add the orange zest. Increase heat to medium–high and bring to a rolling boil; cook for exactly 2 minutes after it starts boiling.
Return the browned chicken to the casserole and gently toss to distribute evenly. Cover with the lid and transfer the casserole to the preheated oven; bake for 25 minutes.
Remove the casserole from the oven and let it rest, covered, for 5 minutes. Remove the cinnamon, star anise and thyme stalks, fluff the rice with a fork, then scatter chopped parsley and toasted nuts (if using) before serving.