Whisk sugar, yolks, and salt in a medium bowl until well blended, about 1 minute. Gradually whisk hot milk mixture into yolk mixture. Return to saucepan; stir over medium-low heat until custard thickens and a thermometer registers 170°F-175°F, about 5 minutes (do not boil). Strain into a medium bowl. Stir in cream. Chill custard until cold, at least 2 hours.