01 - Preheat the oven to 350°F and line two baking sheets with parchment paper.
02 - Place butter in a medium saucepan over medium heat. Cook, stirring constantly, until butter foams and turns deep golden brown with a nutty aroma, about 4-6 minutes. Remove from heat and cool for 10 minutes.
03 - Whisk together flour, oats, baking soda, salt, and cinnamon in a medium bowl until well blended.
04 - Combine browned butter, brown sugar, and granulated sugar in a large bowl. Beat until thoroughly combined. Add eggs one at a time, mixing well after each addition. Stir in vanilla extract.
05 - Gradually add dry ingredients to wet mixture, mixing until just combined. Fold in chocolate chips or raisins and nuts if using.
06 - Scoop dough by rounded tablespoons onto prepared baking sheets, spacing approximately 2 inches apart.
07 - Bake for 10-12 minutes until edges are golden brown and centers are just set. Cool on baking sheets for 5 minutes before transferring to a wire rack to cool completely.