Combine 1½ cups heavy cream, 1 cup whole milk, ¼ cup sugar, and a pinch of kosher salt in a medium saucepan.
Split ½ vanilla bean lengthwise and scrape in seeds; add pod (or use 1 tsp 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 ¼ cup sugar in a medium bowl until pale, about 2 minutes. Gradually whisk in ½ 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.