Bring butter and eggs to room temperature (about 30 minutes). Meanwhile, measure all dry ingredients and set aside.
In a large mixing bowl, beat the softened butter, brown sugar, and granulated sugar until light and fluffy (about 3-4 minutes).
Add eggs one at a time, beating well after each addition. Then mix in the vanilla extract.
In a separate bowl, whisk together the flour, baking soda, cinnamon, and salt. Slowly add this mixture to the wet ingredients, mixing on low speed until just combined.
Gently fold in the rolled oats and butterscotch chips (and nuts if using) until evenly distributed throughout the dough.
Cover the cookie dough and refrigerate for at least 30 minutes (or up to 24 hours for better flavor development).
Preheat your oven to 350°F (175°C) and line baking sheets with parchment paper.
Scoop rounded tablespoons of dough and place them 2 inches apart on the prepared baking sheets.
Bake for 10-12 minutes until edges are golden but centers still appear slightly underdone.
Allow cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.