Reserve the duck giblets. Cut the duck in half by cutting either side of the backbone and through the breastbone.

Then cut each half between the leg and breast to make four portions. Remove and reserve the wing tips for the stock, along with the backbone.

Prick the skin of the portions several times with a metal skewer and then place them on a roasting rack in a roasting tin. Roast the duck portions for 1 hour.

Roughly chop the onion. Using a vegetable peeler, cut strips of zest from the lime or lemon.

To make a good stock, place the onion, giblets, backbone, wing tips, bay leaf and half the zest in a saucepan with about 1 1/2 pints (850 ml) of water. Cover the pan and simmer for 1 hour.

Cut rest of zest into thin strips. Place in a bowl, cover with boiling water for a few minutes; drain.

Peel the mango and cut away the flesh. Cut the large pieces into small cubes and then scrape any remaining fruit from the stone. Put to one side.

Reserving 1/2 pint (285ml) of stock, strain the pan. Mix the cornflour with a little water; stir into the stock.

Stir over a medium heat until thickened. Add the mango and zest, then season to taste.