Place the plums in a shallow, heavy-bottomed saucepan.
Dust the icing sugar over the fruit and add three tablespoons of water, the rose syrup, lime juice and vanilla pod to the pan.
Put over a low heat and cover with a round of baking paper so that none of the liquid can evaporate. Cook for about 25 minutes until the fruit just holds its shape, but has gone incredibly soft. Do watch the plums like a hawk as they cook quicker than you think and will collapse very easily.
Serve with biscuits and crÃ¨me fraiche.