In a small bowl add raisins. Pour 1 tablespoon rum and enough grape juice to cover the raisins. Cover; let stand at room temperature 4 hours or overnight. Take the can of coconut milk and place it in the refrigerator for at least 4 hours but overnight is best.
Place a large mixing bowl in the freezer.
In a large mixing bowl, whip the cold coconut milk until it becomes fluffy. Set aside. Whip the heavy cream until it forms peaks using the bowl from the freezer. Pour condensed milk in a large bowl, add in a small amount of the whipped cream and remaining rum. Whisk to combine.
Combine the remaining coconut milk and the whipped cream. Add the raisins, grape-nut, nutmeg. Whip until fully incorporated.Taste and adjust flavors as needed.
Transfer to a freezer-safe container and cover loosely with plastic wrap. Freeze overnight for best results.
Set out for at least 20 minutes prior to scooping.