In a saucepan, melt the unsalted butter over medium heat. Stir constantly until it turns a deep golden brown and releases a nutty aroma. Remove from heat and allow it to cool slightly.

Set your oven to 350°F (175°C) and line a baking tray with parchment paper to prevent sticking.

In a mixing bowl, whisk together the cooled, browned butter, light brown sugar, white sugar, egg, and vanilla until fully combined and smooth.

In another bowl, sift together the all-purpose flour, baking soda, and salt (if using unsalted pistachios).

Gradually fold the dry ingredients into the wet mixture. Mix just until no flour is visible; avoid overmixing.

Gently fold in the chopped dark chocolate and finely chopped pistachios, ensuring they are evenly distributed throughout the dough.

Use a cookie scoop or tablespoon to drop rounded portions of dough onto the prepared baking tray, leaving enough space for them to spread.

Place the baking tray in the preheated oven and bake for about 10-12 minutes or until the edges turn golden brown.

Remove the cookies from the oven and immediately sprinkle flaky sea salt over the warm cookies. Allow them to cool on the baking tray for a few minutes before transferring to a wire rack to cool completely.

Once cooled, indulge in these delicious cookies with a glass of milk or your favorite beverage.