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 blend, baking soda, sea salt, cocoa powder, and espresso powder until evenly distributed. Set aside.
03 - In a large bowl, beat the softened butter, brown sugar, and granulated sugar with an electric mixer on medium speed until the mixture is light and fluffy, about 2 to 3 minutes.
04 - Add the egg and vanilla extract to the butter mixture, beating until fully incorporated and smooth.
05 - Gradually add the dry ingredient mixture to the wet ingredients, mixing on low speed until just combined. Avoid overmixing.
06 - Using a spatula, gently fold in the chopped pistachios and dark chocolate chips until evenly distributed throughout the dough.
07 - Scoop 1 ½-tablespoon portions of dough and place onto the prepared baking sheets, spacing each about 2 inches apart to allow for spreading.
08 - Bake for 10 to 12 minutes, until the edges are set but the centers remain slightly soft.
09 - Allow the cookies to rest on the baking sheets for 5 minutes, then transfer to a wire rack to cool completely.