Preheat the oven to 220°C.
Dry fry all spices for 2 minutes and grind into a fine powder.
Rub the spice mix over the duck and sear skin-side down in a hot pan until fat renders.
Roast the duck in the oven for 8-12 minutes until cooked through.
Rest the meat for 10 minutes before serving.
Simmer citrus zests in water for 5 minutes, boil to reduce, then stir in the citrus juice.
Caramelize sugar in a pan, whisk in vinegar and stock, and simmer for 5 minutes.
Whisk cold butter into the sauce to thicken.
Sauté the chopped cavolo nero with butter and 30ml of water for 2 minutes.
Slice the duck and serve with the greens and sauce.