Pat the duck thoroughly dry with kitchen paper, then evenly distribute the salt over its surface and inside the cavity. Position the bird breast side up on a wire rack over a tray and allow it to rest at room temperature for 1 hour.

Bring approximately 1½ litres (6 cups) of water to a boil and pour it gently over the entire duck, flipping to cover both sides. Remove any visible feather stubs using tweezers.

Dissolve maltose completely in hot water along with vinegar. Brush a layer over the duck's skin and chill uncovered in the refrigerator for 1 hour. Apply a second coat and refrigerate again, uncovered, for 24 to 48 hours.

Remove the duck from the refrigerator 1 hour before roasting to reach room temperature. Insert the scallions, garlic, apples, star anise, cassia cinnamon, and bay leaves into the cavity. Seal both ends with toothpicks or skewers.

Preheat a fan oven to 200°C/390°F (220°C/425°F for conventional ovens). Place the duck on the center rack breast side up, with a roasting tray below to catch dripping fat. Roast for 15 minutes.

Reduce the oven temperature to 180°C/350°F (200°C/390°F for conventional ovens). Shield the wingtips and leg ends with foil and continue roasting for about 60 more minutes.

Confirm doneness with a meat thermometer inserted into the inner thigh near the breast—the internal temperature should be at least 74°C/165°F.

Allow the duck to rest outside the oven for 15 minutes.

Meanwhile, combine ½ tablespoon of the rendered duck fat with sweet bean sauce and sugar in a small pan. Simmer on low heat until small bubbles form, then transfer to a dish and whisk until emulsified.

Warm the pancakes by steaming them for 3 minutes. Carve the duck into slices.

To serve, spread a bit of sauce on a pancake, add duck slices, scallion strips, and cucumber. Roll and enjoy immediately.