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