Cut the ginger into small cubes.
Rinse the cranberries, then put them into a heavy-based saucepan. Add the ginger and 1 Tbsp of the syrup (or two if you want it really punchy).
Squeeze the mandarin juice and add it to the cranberries, then scoop out the flesh, and roughly chop. Add these to the cranberries, then the sugar and spices.
Stir to combine everything well, then simmer for about 10 minutes until the cranberries are soft and the sauce us thick and sticky. Add more sugar if you think it's not sweet enough.
Let it cool, then chill until serving.