Whisk together cornstarch and ½ cup of the milk in a small bowl to make a slurry.

Combine remaining 1 cup milk, heavy cream, sugar, and salt in a medium saucepan. Cut vanilla bean in half lengthwise. Use the tip of a paring knife to scrape seeds out of pod. Add vanilla seeds to milk mixture. Bring mixture to a simmer over medium heat.

Give slurry a quick whisk to make sure no cornstarch is gathered on the bottom of the bowl. Remove milk mixture from heat and gradually whisk in slurry. Cook, stirring, until mixture comes to a boil and thickens enough to nicely coat the back of a spoon, about 5 minutes. (Do not be tempted to turn up the heat and rush this process.) Transfer mixture to a large bowl and let cool completely before covering and chilling in refrigerator for at least 2 hours.

Strain any lumps that may have formed during the chilling, then pour chilled mixture into an ice cream maker and process according to manufacturer’s instructions. Transfer ice cream to a freezer-safe container, cover, and freeze overnight.