Preheat oven to 350 F. Line two baking trays with parchment paper.
Add the softened butter, brown sugar, and granulated sugar to a large mixing bowl. Using an electric beater, beat until smooth and creamy. Add the vanilla extract and egg and beat until combined, making sure to scrape down the sides of the bowl.
Add flour, baking powder, cinnamon, and salt and beat again until a cookie dough forms. Finally, add the rolled oats and raisins and mix using a spoon or spatula.
Scoop heaped tablespoons of cookie dough onto the prepared baking sheets. Space them out as they will spread when baking.
Bake the cookies for 10-12 minutes or until golden brown on the edges.
Leave the cookies to cool for 5 minutes before moving to a wire rack to cool completely.