Add the sugar and port to a small saucepan along with the zest of one orange and the juice of both.

Bring to the boil and add the cranberries.

Simmer for around 8-10 minutes (keep your eye on them so they don't boil over). The cranberries should still hold their shape, but be soft.

Once cooked, take off of the heat and let cool.

You can freeze or refrigerate the cranberry sauce at this point. Serve to the table at room temperature.