Preheat your oven to 350°F (175°C).
In a large bowl, cream together the softened butter, brown sugar, and granulated sugar.
Add the egg and mix until well combined.
In another bowl, whisk together the flour, baking soda, cinnamon, and salt.
Gradually add the dry ingredients to the wet mixture, blending thoroughly.
Stir in the rolled oats and raisins until evenly distributed.
Drop tablespoon-sized portions of dough onto a baking sheet lined with parchment paper.
Flatten each cookie slightly with the back of a spoon.
Bake in the preheated oven for 12-15 minutes, or until golden brown.
Remove from the oven and allow cooling on a wire rack.