Place the raisins in a container. Pour enough rum to cover the raisins and let the raisins soak overnight. Drain and set aside. This step is only needed if you want rum-flavoured raisins in the cookies.
Sift the plain flour into a medium bowl. Add in the oats, baking powder, and both sugars. Whisk together with a whisk until it’s all combined. Set aside.
In a different bowl, use a fork and whisk the egg and vanilla extract together.
Add the egg mixture into the flour mixture and use a spoon to mix them altogether. The mixture will be crumbly and won’t come together. Add in 2 tablespoons of oil and mix with the spoon until the mixture comes together and form a dough. Add in the additional tablespoon of oil – bit by bit – if the mixture won’t come together and form a dough after adding 2 tablespoons of oil.
Stir in the raisins and chocolate chips into the dough. Cover the dough with clingwrap and refrigerate for 30 minutes up to 2 hours.
Preheat the oven to 190 degrees Celsius. Line baking sheets with parchment paper.
Divide the dough into 12 portions. Roll each portion into a ball and place them on the baking sheet, leaving a 2-inch spacing between the dough for the cookie to expand. Flatten the dough slightly either with the back of a spoon or the heel of your hand.
Bake for 12 – 15 minutes until the cookies have expanded and are pale golden in colour. Let the cookies cool completely before storing them in an airtight container for up to 5 days.