Beat the yolks with the powdered sugar and vanilla sugar until creamy.
Cut the vanilla pod lengthwise and scrape out the pulp.
Bring the vanilla pulp and milk to the boil, remove the milk from the plate and stir the yolk-sugar mixture well into the milk.
Return the saucepan to the plate and heat the custard over low heat for about 3 minutes, stirring constantly.
Then serve as desired.
The milk must not begin to boil, otherwise the yolk will curdle. The vanilla sauce goes well with all kinds of pastries.