Photograph: Jonathan Gregson
Cut off the duck's wings with a large knife, thoroughly wash the cavity, then pat dry. Using a sharp skewer, make small pricks all over the skin. Place the duck in the sink and carefully pour 150ml boiling water over the skin to blanch and tighten it. Pat the duck dry inside and out.
To make the brining solution, in a large bowl dissolve the 150g sugar and 1 tablespoon of sea salt in 200ml boiled water using a balloon whisk. Mix with 750ml cold water and add the vinegar. Put the duck in the bowl and turn over to cover with the solution. Marinate in the fridge for 3 hours, turning the duck over halfway through. Brining helps to keep the meat juicy as it cooks and gives the duck a tangy flavour.
Remove the duck from the brining solution and pat dry inside and out. Discard the brine. For authenticity, insert a meat hook near the neck and hang the duck in a cool, dry place for 8 hours or overnight. Alternatively, put it on a rack above a dish in the fridge. Bring the duck to room temperature before cooking.
When you're ready to cook the duck, preheat the oven to 150°C, fan 130°C, gas 2. Combine the 50g sugar, sea salt flakes and five-spice, then rub it all over the duck, inside and out. Stuff the duck cavity with the ginger, shallots and star anise. Seal the opening with a stainless steel skewer.
Place the duck, breast-side up, on a roasting rack over a roasting tin. Roast for 1 hour 15 minutes, turning over halfway through. Increase the heat to 240°C, fan 220°C, gas 9, turn the duck breast-side up again and drain off the fat. Cook for a further 15-20 minutes to crisp up the skin.
If you like your duck to be even crispier, heat 500ml of groundnut oil in a pan until a cube of bread dropped into it turns golden brown in 15 seconds. Carefully place the duck, still on the roasting rack, over a large hot wok and carefully ladle the oil over the duck until the skin turns golden brown
Remove the skewer, transfer the duck to a serving platter and carve it at the table. Serve with the hoisin or plum sauce, spring onions and cucumber. To eat, place a little duck in the centre of a lettuce leaf, drizzle with sauce, add some spring onion and cucumber, then roll up and eat.
Get ahead: you need to start this recipe the day before.