In a large saucepan, mix the egg yolks with the sugar.
Gradually whisk in the heavy cream and milk. Place the saucepan over low heat and continue whisking until the mixture thickens slightly. Do not boil. Remove the custard from the heat and cool.
Stir in the vanilla extract and 1/4 cup of the rum. Cool completely.
Pour the custard base into an airtight container and chill in the refrigerator at least 8 hours before churning.
Before churning, combine the raisins with the remaining 1 cup of rum in small saucepan. Place over low heat for 5 minutes. Remove from the heat and allow to cool completely. (Raisins will plump and absorb most or all of the rum).
When ready to prepare the ice cream, churn according to the manufacturer’s directions.
About 15 minutes into the churning process, add the plumped and cooled rum raisins to the machine.
Spoon the churned ice cream into a freezer safe container. Freeze until set, at least 2 to 4 hours.