01 - Melt butter in a saucepan over medium heat, stirring frequently. Cook until butter foams and solids turn golden brown with a nutty aroma, approximately 5–7 minutes. Remove from heat and let cool for 15 minutes.
02 - In a medium bowl, whisk together gluten-free flour blend, baking soda, cream of tartar, and salt until thoroughly combined.
03 - In a large bowl, mix cooled brown butter, granulated sugar, and brown sugar until well incorporated. Add eggs and vanilla extract, mixing until smooth and creamy.
04 - Gradually incorporate dry ingredients into wet mixture, stirring until dough forms. Cover and refrigerate for at least 20 minutes, up to 1 hour for best results.
05 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
06 - In a small bowl, stir together granulated sugar and ground cinnamon until evenly mixed.
07 - Scoop tablespoon-sized portions of chilled dough and roll into balls. Coat each ball thoroughly in the cinnamon-sugar mixture.
08 - Place coated dough balls on prepared baking sheets, spacing 2 inches apart. Gently flatten each ball slightly with your palm.
09 - Bake for 9–11 minutes until edges are set but centers appear slightly underbaked. Let cool on pan for 5 minutes, then transfer to wire rack to cool completely.