Preheat the oven to 175°C (350°F). Line a baking sheet with parchment paper.

In a bowl, whisk together oats, flour, baking soda, cinnamon, and salt. Set aside.

In a larger bowl, cream softened butter, brown sugar, and granulated sugar until light and fluffy. Mix in the egg yolk and vanilla extract.

Gradually add the dry ingredients to the wet ingredients, stirring until combined. Fold in the raisins.

Scoop tablespoon-sized portions of dough onto the prepared baking sheet, spacing them 2 inches apart. Flatten slightly with your fingers.

Bake for 10-12 minutes, or until the edges are golden and the centers are still soft. Let the cookies cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.