In a medium saucepan, combine milk, cream, and salt. Add vanilla bean seeds and pod if using. Heat until steaming, not boiling.
In a bowl, whisk together egg yolks and sugar until pale and thick.
Slowly temper the egg mixture by whisking in a ladleful of hot milk mixture, repeating a few times.
Return the tempered mixture to the saucepan.
Cook on low, stirring constantly, until the custard coats the back of a spoon (about 5–7 minutes). Do not boil.
Strain through a fine-mesh sieve into a clean bowl. Remove vanilla pod. If using vanilla extract, stir it in now.
Cool to room temperature, cover, and refrigerate at least 4 hours or overnight.
Churn in an ice cream maker for 20–25 minutes.
Transfer to an airtight container and freeze at least 2 hours before serving.