Put the milk and cream in a heavy-based saucepan. Lightly rub the vanilla beans between your fingertips to soften them.
Cut the vanilla pods in half lengthways and put them in the saucepan.
Put the saucepan over medium heat and bring the milk and cream just to simmering point.
Remove from the heat. Whisk the egg yolks with the sugar in a bowl until light and foamy. Whisk in a little of the warm milk and cream. Add the remaining liquid, reserving the vanilla beans, and whisk to combine.
Return the mixture to the cleaned saucepan. Cook over a medium heat, stirring constantly with a wooden spoon, until the mixture thickens and coats the back of the spoon.
Strain into a bowl. Scrape the vanilla seeds from the split pods into the mixture and stir through.
Allow to cool before churning in an ice-cream machine according to the manufacturer's instructions.