1 ½ cups whole milk
1 teaspoon vanilla
4 large egg yolks
½ cup sugar
2 Tablespoons cornstarch
2 Tablespoons unsalted butter
Over medium heat warm 1 ½ cups milk in a saucepan until small bubbles appear around the edge.
In a medium sized bowl mix together 4 egg yolks, ½ cup sugar, 1 teaspoon vanilla and 2 Tablespoons cornstarch. Whisk together until smooth.
Slowly whisk in the hot milk.
Return the mixture to the pan and cook over medium low heat, whisking constantly, until the mixture comes to a boil and thickens.
Pour into a clean bowl through a fine mesh sieve.
Stir in the butter until melted.
Cover with plastic wrap, pressing it down on top of the pastry cream. This will prevent a skin from forming on the top.
Refrigerate for at least 2 hours, until chilled.