Place the raisins in a mason jar and pour the rum over them.
Seal the jar and allow the raisins to soak for at least 2 hours.
In a large bowl, cream the butter with both sugars until light and smooth.
Beat in the egg.
Add flour and baking soda, stirring until just combined.
Stir in the oats and raisins, including any liquid remaining in the jar with the raisins.
Cover and refrigerate for 1 hour.
Preheat oven to 350℉ and line a baking sheet with parchment paper.
Remove the dough from the fridge and scoop it into evenly sized dough balls, placing them on the prepared pan about 2 inches apart.
Bake in pre-heated oven for 12-15 minutes or until the cookies are golden and the edges are starting to brown. Centres should still be soft.
Allow cookies to cool on the pan for 2-3 minutes before transferring to a wire rack to finish cooling.
Store cooled cookies in an air tight container at room temperature for up to 3 days.