Put the cream and milk in a saucepan (choose one with a lid). Halve the vanilla pods lengthways and scrape the seeds into the pan, discarding the pods. Set the pan over a medium heat and remove from the heat just as the cream and milk mixture is about to come to the boil. Set aside to cool a little.

Put the egg yolks and sugar into a large bowl, then whisk using an electric mixer or hand-held electric beaters until the mixture is very thick and pale.

Bit by bit, pour the warm cream and milk into the sugar and egg mixture, stirring with a wooden spoon as you go. Once it is thoroughly combined, return the mixture to the saucepan. Set the pan over a medium heat, stirring constantly. The mixture will begin to thicken as the eggs start to cook. Once it is on the edge of coming to the boil, remove the custard from the heat and move the pan to a cool surface.

Stir the custard constantly for about 5 minutes to ensure it stays smooth.
Cover the pan with the lid and allow the custard to cool down for about 15 minutes, stirring frequently. Add the lime zest and juice, and the chopped basil leaves, and stir them through. Cover the custard again, then set it aside for 1–2 hours to cool completely. During this time the flavours will develop and amalgamate.

Transfer the cooled custard to a shallow container, making sure the basil is evenly distributed. Put it in the freezer for at least 3 hours. Or, if you have an ice-cream maker, churn as instructed before putting it in the freezer.

Twenty minutes before serving, take the ice cream out of the freezer to soften
a little. Scoop it into individual bowls and eat with a teaspoon.