In a medium saucepan, off heat, whisk together egg yolks, sugar, and salt until blended. Gradually whisk in milk.
Cook over medium, stirring constantly with a wooden spoon, until custard thickens slightly and evenly coats back of spoon (it should hold a line drawn by your finger), 10 to 12 minutes.
Stir 1 vanilla bean (split and scraped) or 2 teaspoons pure
vanilla extract into custard. If using bean, cover custard and let stand 30 minutes.
Pour custard through a fine-mesh sieve into a bowl set over ice. Stir in cream. Let stand, stirring occasionally, until chilled. Churn in an ice cream maker according to manufacturer's instructions. Transfer ice cream to a resealable plastic container and freeze until firm, about 2 hours (or up to 3 months).