- In a saucepan, heat the milk over medium heat until it starts to simmer. 
- In a mixing bowl, whisk together the sugar and cornstarch. 
- Gradually add the hot milk to the sugar mixture, whisking constantly to avoid lumps. 
- Return the mixture to the saucepan and cook over medium heat, stirring constantly, until it thickens. 
- Remove from heat and stir in the vanilla extract. 
- In a separate bowl, beat the egg yolks. Slowly add a small amount of the hot mixture to the yolks, whisking constantly. 
- Pour the egg yolk mixture back into the saucepan and cook for another 2-3 minutes, stirring constantly. 
- Pour the custard into serving dishes and let it cool before serving.