Preheat the oven to 350°F (175°C). Line a baking sheet with parchment paper or lightly grease it.
Mix the dry ingredients: In a medium bowl, whisk together 1 ½ cups of rolled oats, 1 cup of all-purpose flour, 1 tsp baking soda, ½ tsp cinnamon, and a pinch of salt.
Cream the wet ingredients: In a large bowl, cream together ½ cup of softened butter, ½ cup of brown sugar, and ¼ cup of granulated sugar until light and fluffy. Add in 1 large egg and 1 tsp vanilla extract, mixing until well combined.
Combine wet and dry ingredients: Gradually add the dry ingredients to the wet mixture and stir until just combined.
Add raisins: Fold in 1 cup of raisins (or other dried fruit, if desired).
Form the cookies: Scoop out tablespoon-sized portions of dough and place them on the prepared baking sheet, spacing them about 2 inches apart.
Bake the cookies: Bake for 10-12 minutes or until the edges are golden brown and the centers are set.
Cool and serve: Allow the cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.