Preheat your oven to 350°F (175°C) and line your baking sheets with parchment paper.

In a food processor, pulse half of the pistachios until they resemble a fine paste.

In a medium bowl, whisk together the flour, baking powder, baking soda, and salt.

In a large mixing bowl, cream the butter, light brown sugar, and granulated sugar together until light and fluffy.

Add the egg yolks and vanilla extract to the mixture, mixing until pale and combined.

Gradually mix in the flour mixture until just combined, being careful not to overmix.

Fold in the chopped dark chocolate and remaining pistachios.

Scoop balls of dough onto the prepared baking sheets, spacing them 2 inches apart.

Bake for 10-12 minutes until the edges are just set.

Cool on the baking sheets for 5 minutes before transferring to a wire rack, garnishing with flaky sea salt if desired.