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