Plum ripple ice cream with walnuts

Method

1. Heat the oven to 160°C fan/gas 4. Put the walnuts on a baking tray in a single layer, then toast in the oven for 8 minutes. Roughly chop and set aside.
2. Pour the milk and cream into a saucepan, then add the toasted walnuts, split vanilla pod (or paste) and a pinch of salt. Put over a low heat to warm through, stirring occasionally. Meanwhile, use a balloon whisk to whisk the egg yolks and sugar in a separate heatproof bowl until pale and smooth.
3. When the milk mixture begins to simmer, remove from the heat and slowly pour around a third of it over the yolks to temper them (see tips), whisking constantly to combine. Gradually pour in the remaining milk, still whisking, then transfer the mixture back to the pan.
4. Put the custard over a low-medium heat. Whisk regularly until the mixture thickens and coats the back of a spoon (if you have a thermometer, you’re aiming for 80-85°C). Remove from the heat and leave to cool, then transfer to the fridge to chill completely. (You can sit the pan in a bowl of iced water to speed up this process.)
5. While you wait for the ice cream base to chill, put the plums and sugar in a saucepan over a medium heat. Cook for 15 minutes, stirring occasionally, until the fruit breaks down into a thick, syrupy jam. Pass the jam through a fine sieve set over a bowl, using the back of a spoon to push the pulp through, then set aside.
6. Once the ice cream base is chilled, pick out and discard the vanilla pod, then churn the base mixture in an ice cream maker according to the manufacturer’s instructions (see Know How). Once the mixture solidifies, drizzle in a little of the plum ripple and fold it through in the machine a few times to create a ripple effect. Freeze the ice cream, then serve in scoops with more ripple drizzled over.