2 cups milk
¼ cup sugar
2 egg yolks
1 egg
⅓ cup sugar
¼ cup cornstarch
2 Tablespoons butter
2 teaspoon vanilla extract
Stir together milk and 1/4 cup sugar in a heavy saucepan. Bring to a boil over medium – high heat.
In a separate bowl, whisk together egg yolks and egg. Stir together 1/3 cup sugar and cornstarch in a separate bowl; stir into eggs until smooth.
Pour boiled milk into egg mixture in a thin stream while mixing so eggs do not cook. Return egg mixture to the saucepan; slowly bring to a boil, stirring constantly to prevent curdling and scorching.
When mixture thickens, remove from the heat and stir in butter and vanilla until thoroughly blended. Pour into a heat-proof container; cover tightly to prevent a skin from forming. Refrigerate until chilled before using.