In a medium saucepan, heat the whole milk over medium heat until it just begins to simmer. Remove from heat.
In a medium bowl, whisk together the granulated sugar, egg yolks, cornstarch, and salt until smooth and pale in color.
Gradually pour about 1/2 cup of the hot milk into the egg yolk mixture while whisking constantly to temper the eggs.
Slowly pour the tempered egg mixture back into the saucepan with the remaining hot milk, whisking continuously.
Return the saucepan to medium heat and cook, stirring constantly, until the mixture thickens and comes to a gentle boil, about 5 to 7 minutes.
Remove the saucepan from heat and stir in the vanilla extract.
Pour the custard into 4 individual serving cups or ramekins.
Allow the custard cups to cool to room temperature, then cover with plastic wrap and refrigerate for at least 2 hours until set.
Serve chilled and enjoy your classic vanilla custard cups.