01 - Preheat oven to 350°F. Line two baking sheets with parchment paper and set aside.
02 - In a medium bowl, whisk together the gluten-free flour blend, baking soda, and fine sea salt until evenly distributed.
03 - In a large bowl, beat the softened butter, brown sugar, and granulated sugar using an electric mixer on medium speed until light and creamy, approximately 2 minutes.
04 - Add the egg and vanilla extract to the creamed mixture, beating until fully combined and smooth.
05 - Gradually add the dry ingredient mixture to the wet ingredients, mixing on low speed just until the flour is incorporated. Avoid overmixing.
06 - Using a spatula, gently fold the chopped pistachios and dark chocolate pieces into the dough until evenly distributed.
07 - Scoop tablespoon-sized portions of dough onto the prepared baking sheets, spacing them about 2 inches apart. Gently flatten each mound with your fingers for a crispier finish.
08 - Bake for 12 to 14 minutes, rotating sheets halfway through, until the edges are golden brown and the centers are just set.
09 - Allow the cookies to cool on the baking sheets for 5 minutes, then transfer to a wire rack to cool completely before serving.