Prepare the Pistachios: Add half of the pistachios (⅓ cup) to a food processor and pulse into fine crumbs – these will flavor the entire cookie dough. Set aside. Pulse the remaining ⅓ cup pistachios just a few times to roughly chop them for texture. Set aside separately.

② Melt & Cool: Melt the butter just until barely melted, then set aside to cool to room temperature. This step is crucial for the perfect cookie texture – too hot and it will affect your dough consistency.

③ Combine Dry Ingredients: In a small bowl, whisk together the flour, baking soda, and salt. Set aside until ready to use.

④ Create the Base: In a stand mixer or large bowl with a hand mixer, combine the cooled melted butter with both brown and granulated sugars until well mixed. Add the egg, egg yolk, and vanilla extract, mixing until just combined. Stir in the fine pistachio crumbs you made earlier.

⑤ Bring It Together: Add the dry ingredients to the wet mixture and stir until just combined. Fold in most of the chopped pistachios and chocolate chunks, reserving some for topping the hot cookies later. The dough will be soft, so refrigerate for at least 30 minutes or up to 2 days.

⑥ Bake to Perfection: Preheat oven to 350°F and line a baking sheet with parchment paper. Divide the chilled dough into 18 balls (about 60 grams each) and place 2 inches apart. Bake for 10-14 minutes until set on top. Immediately upon removing from the oven, press additional chocolate pieces and chopped pistachios onto each cookie and sprinkle with flaky sea salt. Cool on the baking sheet for 10-15 minutes before transferring to a wire rack.