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 for 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 thoroughly combined. Add eggs one at time, mixing well after each addition. Stir in vanilla.
05 - Gradually add dry ingredients to wet mixture, mixing until just combined. Fold in chocolate chips or raisins and nuts if desired.
06 - Drop 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 barely set. Cool on baking sheets for 5 minutes before transferring to wire rack to cool completely.