For the ice cream, pour the cream and milk into a large saucepan, whisk in the vanilla pod and seeds and bring to the boil. As soon as the mixture is boiling, remove the pan from the heat. Remove the vanilla pod (it can be rinsed, dried and re-used in another recipe).
Whisk together the egg yolks and caster sugar until pale and creamy. Pour over the hot milk and cream mixture, whisking continuously, until the mixture is smooth and well combined.
Return the mixture to a clean saucepan and heat over a low heat for 15-20 minutes, stirring continuously, until the mixture is thick enough to coat the back of a spoon.
Remove the pan from the heat and transfer the custard to a clean bowl. Cover the surface with cling film to prevent a skin from forming, then set aside to cool for 30 minutes.
Meanwhile, for the ripple sauce, place the fruit, sugar and water into a large pan and bring the mixture to the boil, stirring regularly. Reduce the heat until the mixture is simmering, then continue to simmer for 8-10 minutes, or until the fruit has broken down.
Strain the fruit mixture through a sieve into a clean pan, squeezing any additional juice out of the fruit by pressing it down with the back of a spoon.
Return the strained fruit juice to the heat and bring it to a simmer. Continue to simmer until the mixture resembles a thick syrup. Set aside until completely cooled.
Pour the cooled custard into an ice-cream machine and churn according to the manufacturer's instructions, until thick and smooth.
Spoon a third of the ice cream mixture into a lidded freezable container. Spoon over half of the cooled ripple sauce.
Repeat the process until the container has three layers of ice cream and two layers of ripple sauce. Using a blunt knife, marble the ice cream and ripple sauce lightly, then cover the container with a lid and freeze for 3-4 hours, or until solid.
Remove the raspberry ripple ice cream from the freezer and leave to stand at room temperature for 10 minutes before serving.