Cantonese Roast Duck and Duck Fat Potatoes

Two days before: Brine The Cavity

1. Pat the duck dry. Holding the skewer almost parallel to the skin, prick the skin all over, especially across the breast and thighs where the fat is thickest. Go through the fat only and stop before the meat, or juices will seep out during the cook. Lightly score the breast in a crosshatch pattern without cutting into the meat.
2. Rub about one-third of the kosher salt (1½ tsp) inside the cavity, working it into the backbone and thigh areas. Don't salt the skin yet, since scalding will wash it off. Set the duck on the rack over the tray and refrigerate it, uncovered.

The night before: Rub, Scald and Dry

1. Stir together the sugar, five-spice, white pepper and ½ tsp kosher salt. Rub the mixture over the inside of the cavity, into the backbone and around the thighs.
2. Set the duck breast-up on the rack in a clean sink. Bring a full kettle to a rolling boil and pour it slowly over the whole bird in two or three passes, until the skin tightens and turns slightly glossy. Flip the duck and scald the back and legs the same way.
3. Pat the duck completely dry inside and out, including under the wings. Season the skin evenly with the remaining kosher salt (about 3½ tsp). Return the duck to the rack and refrigerate it, uncovered, overnight.

Cook day: Glaze and Dry

1. In the morning, stir the maltose and hot water together until smooth, then add the vinegar and Shaoxing. Brush a thin coat over the skin, let it dry for 10 minutes, then brush on a second thin coat.
2. Return the duck to the fridge, uncovered, or set it in front of a fan, and let it dry for 3 to 4 hours. The skin should feel tacky and look lacquered before it goes near the fire.

Cook day: Truss and Hang

1. About 1½ hours before cooking, light the fire so it has burned down to a bed of embers by the time the duck goes up. Take the duck out of the fridge 45 to 60 minutes before hanging.
2. Truss the duck. Tuck the wing tips behind the back and wrap them in foil so they don't burn. Pull the neck skin over the back and pin it with the metal skewer. Tie the legs tightly across the cavity with twine so the bird hangs compact.
3. Set the double meat hook into the neck cavity, under the backbone, so the duck hangs neck-up with the legs closest to the heat. Loop a length of twine under the wings and up to the chain as a backup sling in case the hook tears through as the skin softens.
4. Hang the duck over the drip pan, with the embers to the back or side rather than directly underneath. Check the heat by holding your hand at duck height: you should manage 5 to 7 seconds. Lower the chain to increase the heat, or raise it to slow the cook. Give the swivel a turn every 10 to 15 minutes so the duck colours evenly.

Potatoes

1. While the duck cooks, put the potatoes in a pot of cold, well-salted water. Bring it to a boil and cook for 8 to 10 minutes, until a knife meets slight resistance. Drain, let the potatoes steam dry for a few minutes, then shake them in the pot to rough up the edges.
2. Once the duck is rendering steadily and fat is collecting in the pan (usually 45 minutes to an hour in), add the potatoes to the drip pan. Toss them in the fat every 15 minutes.

Finish

1. Start checking the temperature after about 2 hours. Probe the thickest part of the thigh without touching the bone. Take the duck off at 78°C (172°F). It will rise to about 80°C (175°F) as it rests. If the breast darkens before the thighs are ready, raise the duck or tent the breast loosely with foil.
2. Rest the duck, uncovered, on a board or rack for 15 to 20 minutes. Don't tent it, or the skin will steam and soften.
3. While the duck rests, heat the cast iron skillet over direct heat. Add the potatoes with a few spoonfuls of the rendered fat and fry them, turning, until crisp and deep golden. Season with flaky salt.
4. Carve the duck and serve it with the potatoes.