Mix up the sugar, salt and cornstarch in a bowl. In a heavy saucepan, scald the milk over medium heat. Stir gently until the little bubbles just start to rise around the edges. Then slowly whisk in the dry mix. Cook, constantly stirring to make sure the bottom doesn't scorch, while the pudding thickens, 15-20 minutes.
When it coats the back of a metal spoon, take it off the heat and stir in the vanilla and butter until the butter is melted and mixed through.
Drop 5-10 (or 50!) chocolate chips in the bottom of each of 4 serving dishes and pour 1/2 cup of pudding over them. Let it chill, (but not too long!) just until cool enough not to burn your tongue.
Dip your spoon into the melted chocolate at the bottom so it flavors every bite of the still-warm pudding.