Stir in the pureed plums. Lightly whip the cream and fold into the mixture with the chopped white chocolate. Pour into a freezer proof container. Cover with a lid. Place in the freezer. After about 1 hour. remove the ice cream from the freezer and stir - this will help disperse the chocolate pieces through the ice cream, otherwise you may find they have all sunk to the bottom. Return the ice cream to the freezer for a further 4-5 hours until it has frozen.