Preheat your oven to 180°C (350°F). Pat the duck dry with paper towels, then rub it all over with the softened butter. In a small bowl, mix salt, black pepper, ground cinnamon, and ground ginger. Rub this spice mixture onto the duck, ensuring an even coating on both the outside and inside the cavity.

Place the duck, breast side up, on a rack in a roasting pan. Pierce the skin all over with a fork to allow the fat to render out. Roast the duck in the preheated oven for 1.5 to 2 hours, basting occasionally with its own rendered fat. The skin should become crispy and golden, with the internal temperature reaching 74°C (165°F).

While the duck is roasting, prepare the orange sauce. In a medium saucepan, combine the sugar and vinegar. Heat over medium-high until the sugar dissolves, then reduce the heat to low and let the mixture simmer until it reduces by half and becomes slightly syrupy.

Add the orange juice and zest to the saucepan, followed by the orange marmalade and chicken broth. Stir well, then bring the sauce to a boil. Reduce heat to low and simmer for about 10-15 minutes, allowing the flavors to meld and the sauce to reduce slightly.

If you'd like to thicken the sauce, mix 1 tablespoon of cornstarch with 2 tablespoons of cold water, then stir this slurry into the sauce. Simmer for a few more minutes until the sauce thickens to your desired consistency. Season with salt and black pepper to taste.

Remove the saucepan from the heat and stir in the cold butter cubes, one at a time, whisking continuously. This will give the sauce a glossy finish and add a rich flavour. Keep the sauce warm on low heat while the duck finishes roasting.

Once the duck is fully roasted, remove it from the oven and let it rest for about 10 minutes. This resting period helps retain the juices, ensuring a tender and succulent result. While resting, skim off any excess fat from the pan juices, and reserve a bit of the fat to drizzle over the duck before serving.

Carve the duck into individual portions. Pour the warm orange sauce over the duck and serve immediately. Garnish with fresh orange slices or a sprinkling of additional orange zest for a bright citrusy presentation. Pair the dish with roasted potatoes or a simple green vegetable, such as haricots verts, to complement the rich flavours.