If you are using fresh cranberries rinse them toughly or in the case of frozen defrost and drain well. Bring to the boil the orange juice, liqueur, port and sugar, when bubbling add the cranberries and return to the boil.
On a low heat, simmer gently for a further ten minutes until slightly thickened, remove from the heat and stir in the jelly crystals, allow to stand for at least 15 minutes.
When cooled slightly turn into either individual serving moulds (i.e. small ramekins) or a fancy jelly mould to use as a centre piece for the Christmas table.
This sauce can be kept covered in the fridge for up to a week and is ideal served with turkey, duck, goose and any game birds.