Whisk together in a medium saucepan:
Gradually whisk in:
Bring to a simmer over medium heat, stirring occasionally to dissolve the sugar. Whisk together in a medium heatproof bowl:
Slowly pour about half the hot milk mixture into the eggs, whisking constantly. Pour this mixture back into the saucepan and cook over medium-low heat, stirring constantly, until the custard reaches 175°F and coats the back of a spoon. Do not allow the mixture to boil. Remove the pan from the heat and strain the custard through a fine-mesh sieve into a medium bowl. Stir in:
Refrigerate the ice cream base until cold, overnight if possible, or quick-chill in an ice water bath.
Pour the base into an ice cream maker and freeze as directed. If desired, when the ice cream is almost frozen, stir in:
Transfer to a container with a tight-fitting lid and freeze for at least 4 hours to harden.