36 to 48 hours before preparing the ice cream, add the raisins, rum and orange rind to a small container with a lid. Let sit at room temperature, shaking occasionally. (See Notes.)
Preparation Day:
Create an ice bath: fill a large bowl with water and ice, and set aside. You want the large bowl with 1 cup heavy cream (and strainer) to sit in it comfortably and not take on water as you’re stirring.
Warm the milk, sugar, 1/2 cup heavy cream and salt in a medium saucepan (2 to 3 quarts) over medium-low heat until it reaches 170°F.
Pour the remaining 1 cup heavy cream into a large bowl and set a mesh strainer over the top of the bowl.
In a separate medium bowl, whisk together the egg yolks. Slowly pour the warmed milk mixture into the egg yolks, whisking constantly.
Then scrape the warmed egg yolks back into the saucepan. Stir the mixture constantly with a heatproof spatula over medium heat, scraping the bottom as you stir, until the mixture thickens and coats the spatula, 2 to 3 minutes.
Pour the custard through the strainer and into the remaining heavy cream. Place the bowl in the ice bath. Stir until cool, then chill the mixture thoroughly in the refrigerator, at least 1 hour and up to overnight.
When you're ready to freeze the ice cream, drain the raisins over a bowl and reserve the rum. Discard the orange rind. Measure the drained rum and add more, if necessary, so that you have a total of 3 tablespoons. Stir the rum into the custard and discard (or drink!) any extra rum.
Freeze the mixture in your ice cream maker according to the manufacturer’s instructions. During the last few minutes of churning, add the raisins.
Transfer to a freezer-safe container and freeze for at least 4 hours before serving. Can be prepared up to a week in advance.
Notes
If you only have a few hours to plump the raisins, heat the raisins, rum, and orange rind in a small saucepan. Let simmer for 2 minutes, then remove from the heat. Cover and let stand for 2 to 3 hours.
The rum lowers the freezing point of the ice cream, so it’s very soft even if it’s been frozen for a while. It’s best served in a bowl and not on a cone.