1. Cut the plums neatly in half and remove the stones.
2. Put into a baking dish or casserole, sprinkle with the sugar (the amount required will depend on the sweetness of the plums) and pour the port on top.
3. Cover securely with a lid or foil and bake in a cool oven at 150°C, Gas 2, for 45-60 minutes or until the plums are tender.
4. Serve hot, or lightly chilled.