Heat 2 tbsp of oil in a large casserole and lightly brown the nuts on all sides. Drain on kitchen roll. Fry the sliced onion in the same oil until dark brown and caramelized, then drain and reserve. Add the cumin, pepper, cassia, cardamom and mace to the oil (adding a drop more if needed) and gently fry for 30 seconds, or until you can smell the aroma - don’t burn them. Stir in the chopped onion, ginger and garlic and gently fry until the onion has softened. Tip the rice into the pan and turn through with the spiced onion to coat. Add enough water to cover the rice by 2cm, salt it, then cover and bring to the boil. Turn down the heat to very low and simmer for 6 minutes. Turn off the heat and leave covered for 10 minutes. Meanwhile, heat 2 more tbsp oil in a non-stick frying pan. Rub the fish with salt and a few grinds of pepper and fry skin-side down for 1 minute, then remove and drain. They won’t be cooked, just crisped. Bed down the fillets in the rice pan so they’re layered into the rice and covered up, interspersing the layers with the raisins, nuts and caramelized sliced onion. Make holes in the rice with the handle of a wooden spoon, then pour over the coconut milk. Cover and put in a 180°C/350°F/Gas 4 oven for 30 minutes.