1. Spread the breadcrumbs on a baking sheet and sprinkle over the brown sugar. Bake in the oven at 200°C (400°F) mark 6 for about 10 minutes, stirring occasionally until the sugar caramelises and the crumbs are golden. Cool and break down with a fork.
2. Whisk together the fresh double and single creams until stiff. Gently fold in the rum and icing sugar.
3. Pour into a chilled shallow container and freeze for 1 1/2 - 2 hours or until mushy in consistency.
4. Turn into a bowl and mash with a fork or whisk until smooth. Stir in the breadcrumbs Spoon back into the container and freeze until firm.
To freeze Overwrap according to type of container.