In a small, heavy saucepan over high heat, combine the milk and vanilla bean and bring to a simmer. Meanwhile, in a bowl, whisk together the egg yolks, sugar and cornstarch until well blended. When the milk reaches a simmer, remove it from the heat and gradually whisk the hot milk mixture into the yolk mixture. Return the mixture to the saucepan and place it over medium heat. Cook, whisking constantly, until the pastry cream thickens and boils, about 1 minute. Discard the vanilla bean and transfer the pastry cream to a small bowl. Use as directed in specific recipes. Makes 1 cup. Makes a delicious filling for cakes and tarts.