Roughly chop the raisins.
Warm 1/2 cup (125 ml) rum in a small saucepan over low heat. Add raisins and stir 3–5 minutes until plump and glossy; cool completely.
In a large bowl, mix sweetened condensed milk, 1/4 cup (60 ml) rum, and vanilla powder until smooth.
Stir the cooled rum raisins into the condensed milk mixture.
In a separate bowl, whip the cold heavy cream to stiff peaks.
Fold whipped cream into the condensed milk mixture until combined and airy.
Transfer to a freezer-safe container, smooth the top, cover tightly, and freeze at least 6 hours (overnight is great).
Let stand 5–10 minutes at room temperature if needed, then scoop.
Serve immediately.