01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - Whisk together flour, baking soda, salt, and cinnamon in a medium bowl. Set aside.
03 - Beat softened butter, brown sugar, and granulated sugar in a large bowl until light and fluffy, about 2 to 3 minutes.
04 - Add eggs one at a time, beating well after each addition, then stir in vanilla extract.
05 - Gradually add the dry mixture to the wet ingredients, stirring until just combined.
06 - Gently fold in rolled oats, raisins, and walnuts (if using) until evenly distributed.
07 - Drop rounded tablespoons of dough about 2 inches apart onto the prepared baking sheets.
08 - Bake for 10 to 12 minutes until edges are lightly golden and centers appear set.
09 - Cool cookies on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.