-
Whisk 1/4 cup whole milk and the cornstarch in a bowl; set aside.
-
In a saucepan, combine remaining whole milk and reduced fat milk, and bring to a simmer over medium heat.
-
Meanwhile, whisk 1 cup brown sugar, the vanilla extract, salt, and 2 yolks into the cornstarch mixture.
-
Gradually whisk the warmed milk into the cornstarch mixture, then return everything to the saucepan; cook over medium heat to a beginning boil, stirring constantly with the whisk.
-
Cook, stirring constantly, until mixture is thick, 1 minute.
-
Remove from heat, add 1 tablespoon butter, and stir until the butter melts.
-
Chill 3 hours before serving; cover surface with plastic wrap to prevent skin from forming.