01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - Whisk together flour, cocoa powder, baking soda, and salt in a medium bowl until well blended.
03 - Beat butter, brown sugar, and granulated sugar in a large bowl until light and fluffy, approximately 2-3 minutes.
04 - Add eggs one at a time, beating thoroughly after each addition. Mix in vanilla extract until incorporated.
05 - Gradually add dry ingredients to wet mixture, mixing until just combined. Avoid overmixing to prevent tough cookies.
06 - Gently fold in dark chocolate chips, semi-sweet chocolate chips, and chopped pistachios until evenly distributed.
07 - Scoop tablespoon-sized dough balls onto prepared baking sheets, spacing 2 inches apart to allow for spreading.
08 - Lightly sprinkle each cookie with flaky sea salt if desired.
09 - Bake for 10-12 minutes until edges are set but centers remain soft and slightly underbaked.
10 - Let cookies rest on baking sheets for 5 minutes, then transfer to wire rack to cool completely.