Split the vanilla pod lengthways with a sharp knife and scrape out the seeds.
Place the caster sugar, 200g (¾ cup) water, the vanilla pod and the scraped seeds into a medium-sized saucepan. Heat gently, stirring occasionally just to disperse the seeds, so the sugar slowly dissolves into the water.
Bring to the boil and continue gently boiling on a medium heat until it reaches between 110°C- 114°C (230°F-237°F) on a sugar thermometer and forms a syrupy consistency. This usually takes between 15-20 minutes. Keep a close eye on the syrup and check the temperature frequently to avoid overcooking it.
While the syrup is cooking, whisk the aquafaba in a large mixing bowl using an electric whisk (or stand mixer) until it forms stiff peaks.
Once the sugar syrup reaches 110°C- 114°C (230°F-237°F), slowly pour it into the whipped aquafaba in a thin, steady steam, whisking continuously. The mixture will turn thick, glossy and increase in volume.
In a separate bowl, whip the plant-based double cream until it thickens into firm peaks. You will probably find it doesn’t thicken as much as real cream but soft-firm is good enough.
Gently fold the cream into the glossy aquafaba until fully combined.
Cover the bowl and refrigerate overnight to allow the mixture to chill completely.
The following day, remove and discard the vanilla pod.
The recipe makes approximately 1kg of ice cream, so you may find it easier to churn in two batches, depending on the capacity of your ice cream maker. Weigh out half the mixture and return the remaining half to the refrigerator until you’re ready to churn it. It can be kept chilled for a further 24 hours.
Pour the chilled ice cream base into your ice cream machine and churn for 35-40 minutes, or according to the manufacturer’s instructions, until it reaches the consistency of soft-serve ice cream.
Transfer the churned ice cream to a freezer-safe airtight container and smooth the surface. Freeze for at least 8 hours, or preferably overnight, until firm enough to scoop and serve.