Place all the ingredients (except the salt) in a large stock pot and pour over enough water to cover them completely. Place over a medium to high heat and bring to a rapid simmer. Skim off any foam that appears on the surface; keep doing this until the stock stays clear.

Keeping the heat low, gently simmer the stock for about three hours or until reduced by one-third. Leave the stock to cool, then strain through a fine-mesh sieve/strainer. Adjust the seasoning with salt to taste.

Use the quantity needed for your recipe, then you can store the remaining stock in the fridge for a few days or in the freezer in portions for up to three months.

In a small saucepan, bring 100 milliliters/scant 1/2 cup water to the boil. Add the orange and lemon peel, reduce the heat and simmer for two to three minutes or until tender. Strain, reserving the peel. Set aside.

In a separate saucepan, dissolve the sugar in 50 ml/scant 1/4 cup water. Bring to a fast boil, reducing the liquid to a light syrup. Carefully stir the orange and lemon juices into the syrup. Let the sauce reduce a little further and then stir in the sherry vinegar, brandy and orange liqueur.

Warm the stock, then stir in the marmalade until dissolved. Add this stock to the pan with the sauce and cook for a few minutes until all the flavors have mingled. Let it reduce a little more, then add the reserved orange and lemon peel. If the sauce is too thin, add the cornflour/cornstarch paste to thicken. Taste and adjust the seasoning, if needed. Set aside in the pan.

Using a very sharp knife, score the skin of the duck breasts, cutting in two directions to make a diamond-shaped pattern on the surface without slicing into the meat. Season with salt and black pepper.

Place the duck breasts, skin side down, in a cold frying pan/skillet. Place over a medium heat and cook for 12 minutes – as the pan warms, the skin will release its tasty fat and become crispy. Turn over the duck breasts and cook on the other side for a further three minutes (slightly longer if you prefer them less pink). Transfer the duck breasts to a plate, cover to keep warm and leave to rest for 10 minutes; this is important.

When ready to serve, slice the duck breasts, but not too thinly. Warm a serving dish under a hot tap and reheat the sauce. Arrange the sliced duck on the warm serving dish and cover with the hot sauce. Decorate the duck with some of the strips of peel and orange segments.