01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - Whisk together flour, baking powder, baking soda, and fine sea salt in a medium bowl. Set aside.
03 - Beat butter, granulated sugar, and brown sugar until light and fluffy, about 2-3 minutes.
04 - Beat in egg and vanilla extract until well combined.
05 - Gradually add dry ingredients to wet mixture, mixing until just combined.
06 - Fold in chopped pistachios until evenly distributed throughout dough.
07 - Drop tablespoon-sized mounds onto prepared baking sheets, spacing 2 inches apart.
08 - Gently flatten each mound slightly and sprinkle tops with flaky sea salt.
09 - Bake for 11-13 minutes until edges are lightly golden but centers remain soft.
10 - Let cookies rest on baking sheet for 5 minutes, then transfer to wire rack to cool completely.