Combine in a medium saucepan and bring to a simmer over medium-low heat, stirring occasionally to dissolve the sugar:
Beat together in a medium heatproof bowl:
Slowly whisk half the hot milk mixture into the beaten egg yolks, then pour this mixture back into the rest of the milk. Cook over 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. Whisk 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.