In a saucepan stir 2 ½ cups milk, sugar, salt, and vanilla. Stir till simmering.

In a separate bowl whisk cornstarch, flour, egg yolks with the remaining milk. Temper with hot mixture and pour back into saucepan.

Stir constantly while bringing it to a boil and mixture thickens.

Take off heat and stir in butter and vanilla.

Pour through a sieve for a smooth finish.

Store in fridge with plastic wrap touching the top to prevent a skin from forming.

Optional: Fold in whipped cream before using.