Preheat the oven to 350°F (175°C) and line baking sheets with parchment paper.
Cream the softened butter with brown and granulated sugar until light and fluffy.
Beat in the eggs one at a time, then stir in the vanilla until combined.
Whisk together the flour, baking soda, cinnamon, and salt in a separate bowl.
Gradually add the dry ingredients to the butter mixture and mix until just combined.
Fold in the rolled oats and raisins (plus nuts if using) until evenly distributed.
Scoop dough by rounded tablespoons onto prepared sheets, spacing about 2 inches apart.
Optional: chill scooped dough 30–60 minutes for thicker cookies and less spreading.
Bake for 10–12 minutes, until edges are golden and centers look set but still soft.
Cool cookies on the sheet for 5 minutes, then transfer to a wire rack to cool completely.