Heat oven to 350°F. Line two baking sheets with parchment.
Cream the softened butter, brown sugar, and granulated sugar until fluffy, 2–3 minutes.
Beat in the eggs and vanilla until smooth and combined.
Whisk flour, baking soda, salt, and cinnamon in a separate bowl.
Stir the dry ingredients into the butter mixture just until no dry spots remain.
Fold in oats, raisins, and walnuts if using.
Scoop rounded tablespoons of dough onto sheets, spacing about 2 inches apart.
Bake 10–12 minutes, until edges are set and centers look slightly soft.
Cool on the pan 5 minutes, then move cookies to a rack to finish cooling.