Heat the oven to 180°C/350ºF/gas 4. Wash the duck, inside and out, and thoroughly pat dry with some kitchen paper. Place breast-side up in a roasting tray and stuff with the orange halves and the sprigs of rosemary and sage.
Mix the Chinese five-spice with a good pinch of salt and pepper and rub all over the duck, inside and out. Turn the duck breast-side down and pop in the oven for an hour.
Remove the tray from the oven. Carefully spoon all the fat out of the tray and strain through a sieve into a bowl. Leave to cool. Turn the duck over and place it back in the oven for another hour.
After the duck has had 2 hours, remove the tray from the oven and, once again, spoon the fat out of the tray and into the bowl. Leave the duck to cool completely.
Once cool, cut the duck into 4 portions by carefully cutting off the breasts and legs, discarding the carcass. Place in a tall, sterilised jar and push down on the duck to make it a compact layer. Pour the duck fat over the duck, ensuring it is completely covered and seal the jar. Store in the fridge for up to two weeks.
When ready to use the duck, break and remove the fat layer – don’t throw it away though, keep it for roast potatoes. Place the duck in an oven heated to 200°C/400ºF/gas 6 for 20 minutes or until crisp and tender.
I love serving my duck with noodles. All that needs doing is to bring a pan of salted water to the boil. Add the pak choi, sugar snaps and noodles and cook for 4 minutes. Drain and toss with the chilli, sesame oil, lime juice, coriander leaves and some seasoning. Serve with the duck.
If you are going to eat the duck immediately, roast it for 2 hours as described above, then turn the oven temperature up to 200°C/400ºF/gas 6 and cook for another 15 minutes.