Boil the milk on low heat. Mix the yolks with the sugar, salt and starch until homogeneous.
Pour the boiled milk in a thin trickle into the egg mixture while stirring nonstop. Pour this cream back into the container in which you boiled the milk.
Bring to a boil again and boil 2 min. while stirring nonstop.
Remove from the stove, strain through a sieve and add the vanilla. Stir and leave it to cool for 10 min.
Cut the butter into thin pieces and add them to the cream while stirring nonstop.
Leave the cream to cool completely, then you can store it in the fridge for up to 4 days.