In a large chilled bowl, whisk together the milk, sugar (and optional salt) until the sugar is fully dissolved. Stir in the heavy cream and vanilla. Cover and refrigerate 1-2 hours, or overnight.
Turn on the ice cream maker; pour cold milk mixture into the frozen freezer bowl and churn until thickened, about 15-20 minutes. The ice cream will have a soft, creamy texture. For firmer texture, use rubber spatula to fully transfer the ice cream to an airtight container, cover, and place in freezer for at least 2 hours. May need to let ice cream sit at room temperature for 5 minutes before scooping.