Finely chop the mandarin.
Add all ingredients to a saucepan, except the orange liqueur.
Heat it gently over medium heat. Stir well, then bring to a simmer.
Once the cranberries have softened (in about 10-15 minutes), turn up the heat to thicken (use a fork or spoon to mash the fruits a bit).
When you get a sticky, almost jam-like sauce, turn off the heat and let it cool. Add the orange liqueur and remove the cinnamon.
Transfer it to a jar for late ruse, or serve immediately with poultry, game, cold meats, cheese etc.