01 - Preheat the oven to 350°F. Line two baking sheets with parchment paper.
02 - In a medium bowl, whisk together the gluten-free flour, cocoa powder, baking soda, and salt. Set aside.
03 - In a large bowl, beat the softened butter, brown sugar, and granulated sugar with an electric mixer until light and creamy, about 2 minutes.
04 - Add the egg and vanilla extract to the butter mixture, beating until well combined.
05 - Gradually add the dry ingredients to the wet mixture, mixing until just incorporated.
06 - Fold in the dark chocolate chips and chopped pistachios with a spatula.
07 - Scoop tablespoons of dough onto the prepared baking sheets, spacing cookies about 2 inches apart.
08 - Bake for 11 to 12 minutes, until the edges are set but centers appear slightly soft.
09 - Allow cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.