01 - Preheat the oven to 350°F. Line two baking sheets with parchment paper.
02 - Place the butter in a medium saucepan over medium heat. Cook, stirring often, until the butter foams and turns deep golden brown with a nutty aroma, 4-6 minutes. Remove from heat and let cool for 10 minutes.
03 - In a medium bowl, whisk together the flour, oats, baking soda, salt, and cinnamon.
04 - In a large bowl, combine the browned butter, brown sugar, and granulated sugar. Beat until well mixed. Add eggs one at a time, mixing well after each addition. Stir in vanilla.
05 - Gradually add the dry ingredients to the wet ingredients, 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 about 2 inches apart.
07 - Bake for 10-12 minutes, until edges are golden and centers are just set. Cool on the baking sheets for 5 minutes before transferring to a wire rack to cool completely.