2 cups whole milk
1/4 teaspoon kosher salt
1/2 vanilla bean, split lengthwise and seeds scraped (see Cook's Note)
1/2 cup sugar
1/4 cup cornstarch
4 large egg yolks
2 tablespoons unsalted butter, cut into small pieces
Alternatively, you can substitute 1 teaspoon vanilla bean paste or 1 teaspoon pure vanilla extract for the 1/2 vanilla bean.