Soak the Raisins (1/2 cup) in Rum (1 cup) overnight or soak them for a few days in a covered container so the rum does not evaporate. If you’re in a rush, place 1 cup of rum in a deep saucepan with the raisins and place it on a low flame until raisins are plump and saturated.
Put the Caster Sugar (3/4 cup) and yolks of the Egg (4) in a bowl and whisk until creamy/smooth. It will go from the brilliant yellow to a very pale color.
At the same time place the Heavy Cream (2 1/2 cup) and Milk (1 1/2 cup) in a saucepan and let it warm through (almost to a gentle simmer).
Before adding the sugar-egg mixture to the pot, add a little of the warm milk to the bowl with the egg and whisk. Do that a couple times so the egg mixture warms up.
Now add all the egg mixture to the pot and whisk. Add Salt (1 pinch) and Vanilla Extract (1 tablespoon).
When your custard is thick, add the soaked raisins and pour the custard into a bowl and chill for at least 2 hours.
After the custard is properly chilled, add it to your ice cream maker and make it according to the manufacturer’s directions.
This can be served immediately. Enjoy!