Bring the milk to a boil in medium saucepan over a low heat.
Whisk the egg yolks and sugar together until thick and pale.
Pour the hot milk slowly into the yolk mixture, stirring constantly.
Pour back into a clean saucepan and cook over medium heat, stirring constantly with a wooden spoon, until the custard coats the back of the spoon.
Strain the custard into a bowl and stir until cool.
Place the mixture in the refrigerator until chilled.
Once cold, mix in the buttermilk, then churn in an ice cream machine according to the manufacturer's instructions.