Beat softened butter with brown sugar and granulated sugar until light and fluffy.
Add eggs one at a time, mixing well after each addition.
In a separate bowl, whisk together flour, baking soda, cinnamon, and salt.
Gradually add dry ingredients to butter mixture, mixing until just combined.
Stir in oats and chocolate chips or raisins if using.
Chill dough for 30 minutes in refrigerator.
Preheat oven to 375°F and line baking sheets with parchment paper.
Drop rounded tablespoons of dough onto prepared baking sheets, spacing 2 inches apart.
Bake for 10-12 minutes until edges are golden brown.
Cool on baking sheet for 5 minutes before transferring to wire rack.