In a bowl, whisk together the flour, cinnamon, baking soda, and salt. Set aside.
Cream together the butter, brown sugar, and granulated sugar for 1-2 minutes until well combined. Add the egg and vanilla extract and mix until fully combined.
Slowly mix in the flour mixture and continue mixing until just combined, then mix in the oats and raisins until fully combined.
Cover with cling film and leave to rest for 30 minutes.
Meanwhile, preheat the oven to 180°C. Line two large baking sheets with parchment paper or silicone baking mats and set aside.
Once the dough is chilled you need to roll the cookie dough into balls and very gently press down with your hand to flatten each ball of cookie dough. Make sure to leave a little room between each ball of cookie dough as they will spread a little while they bake.
Bake for 10-12 minutes or until the edges of the cookies are lightly golden brown and the top is set. Remove from the oven and cool on the baking sheet for 5 minutes, then transfer the cookies to a wire rack to finish cooling.