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 powder, and salt until evenly distributed.
03 - In a large bowl, beat the softened butter and granulated sugar with an electric mixer until light and creamy, about 2 minutes.
04 - Add the egg, fresh lemon juice, lemon zest, and vanilla extract to the butter mixture. Beat until well combined and smooth.
05 - Gradually add the dry ingredients to the wet mixture, mixing on low speed until just incorporated. Do not overmix.
06 - Gently fold the chopped pistachios into the dough using a spatula until evenly distributed.
07 - Scoop tablespoon-sized portions of dough onto the prepared baking sheets, spacing about 2 inches apart. Gently flatten each ball to about ½ inch thick using your fingers or the bottom of a glass.
08 - Bake for 10 to 12 minutes, or until the edges are golden and the centers are just set.
09 - Let the cookies cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.