In a medium saucepan, whisk together the sugar, cornstarch, and salt. Gradually stir in the milk. Cook over medium heat, stirring constantly, until mixture thickens and begins to boil. Boil, stirring constantly, for 1 minute. Whisk about half of the hot mixture into the lightly beaten egg yolks. Stir the egg yolk mixture back into the saucepan mixture. Boil, stirring constantly, for 1 minute; remove from heat and stir in the butter and vanilla.
Divide evenly among 4 dessert dishes. Chill thoroughly before serving.
Serve with a dollop of whipped cream or whipped topping.
Makes about 6 1/3-cup servings
Calories per serving: 171
Fat per serving: 6.9