Position a rack in the lower third of your oven and heat to 425°F. Set a wire rack inside a rimmed baking sheet or roasting pan.
Using a sharp knife, score the duck skin in a crosshatch pattern, cutting through the skin but not into the meat — this helps the fat render properly. Pierce the skin all over with a fork, focusing on the fattiest areas around the thighs and breast.
Rub the salt and pepper all over the duck, inside the cavity and on the skin. Don't be shy here — duck needs assertive seasoning to balance its richness.
Place the duck breast-side up on the wire rack. The rack keeps the duck elevated so it roasts evenly rather than sitting in its own fat.
Roast for 20 minutes at 425°F, then reduce the temperature to 350°F and continue cooking for about 2 hours more. The duck is done when an instant-read thermometer inserted into the thickest part of the thigh reads 165°F. The skin should be deep golden and crispy.
⏱ 2 hrs 20 min
While the duck roasts, make the sauce: combine the orange juice, chicken stock, marmalade, Grand Marnier, and red wine vinegar in a medium saucepan. Stir to dissolve the marmalade completely.
Bring the sauce to a gentle simmer over medium heat and cook until it reduces by about half — it should coat the back of a spoon lightly. This concentrates all those bright orange flavors.
⏱ 15 min
Whisk the cornstarch with 2 tablespoons of cold water until smooth, then stir this slurry into the simmering sauce. This prevents lumps and ensures a silky texture.
Simmer the sauce for 2 minutes until it thickens to a glossy, coating consistency. Remove from heat and whisk in the cold butter pieces one at a time, then stir in the orange zest. The butter adds richness and shine.
⏱ 2 min
Let the duck rest for 10 minutes before carving — this allows the juices to redistribute. Carve into portions and serve immediately with the warm orange sauce spooned over or alongside.
⏱ 10 min