Step 1

Position a strainer over a medium bowl set in a larger bowl containing ice water. Heat the milk, cream, 1/2 cup of the sugar, and the vanilla seeds and pod in a medium saucepan over medium heat, stirring occasionally to break up the vanilla seeds, until steam appears and the milk is warm (about 175 degrees), about 5 minutes.

Step 2

Meanwhile, whisk the yolks and remaining 1/4 cup sugar in a medium bowl until combined and pale yellow. Whisk half the warm milk mixture into the beaten yolks, 1/2 cup at a time, until combined. Whisk the milk-yolk mixture into the warm milk in the saucepan; set the saucepan over medium heat and cook, stirring constantly with a wooden spoon, until steam appears, foam subsides, and the mixture is slightly thickened or an instant-read thermometer registers 180 to 185 degrees. (Do not boil the mixture, or the eggs will curdle.) Immediately strain the custard into the bowl set in the ice bath; cool the custard to room temperature, stirring it occasionally to help it cool. Cover and refrigerate until an instant-read thermometer -registers 40 degrees or lower, at least 3 hours or up to 24 hours.

Step 3

Add the vanilla extract, if using, and stir well. Pour the custard into the ice cream machine canister and churn, following the manufacturer’s instructions, until the mixture resembles soft-serve ice cream. Transfer the ice cream to an airtight container, press plastic wrap flush against the surface, cover the container, and freeze the ice cream until firm, at least 2 hours. (The ice cream will keep for up to 2 days.)