Combine 1 1/2 cups heavy cream, 1 cup whole milk, 1/4 cup sugar, and a pinch of kosher salt in a medium saucepan. Split 1/2 vanilla bean lengthwise and scrape in seeds; add pod (or use 1 teaspoon vanilla extract). Bring mixture just to a simmer, stirring to dissolve sugar.
Remove from heat. If using vanilla bean, cover; let sit 30 minutes.
Whisk 5 large egg yolks and 1/4 cup sugar in a medium bowl until pale, about 2 minutes. Gradually whisk in 1/2 cup warm cream mixture.
Whisk yolk mixture into remaining cream mixture. Cook over medium heat, stirring constantly, until thick enough to coat a wooden spoon, 2-3 minutes. Strain custard into a medium bowl set over a bowl of ice water; let cool, stirring occasionally. Process custard in an ice cream maker according to manufacturer's instructions.
Transfer to an airtight container; cover. Freeze until firm, at least 4 hours and up to 1 week.
