Gather milk, sugar, cornstarch, salt, egg yolks, vanilla extract, and butter
Whisk cornstarch, sugar, and salt in a saucepan
Slowly whisk in milk until smooth
Cook over medium heat, stirring constantly
In a separate bowl, whisk egg yolks
Temper the egg yolks by slowly adding a little hot mixture while whisking
Pour the tempered yolks back into the saucepan
Continue cooking and stirring until thickened
Remove from heat
Stir in vanilla extract and butter
Pour into serving dishes
Chill until set
Serve cold