In a saucepan over medium heat, melt the unsalted butter until it starts to foam. Continue cooking, stirring occasionally, until the butter turns golden brown and releases a nutty aroma. Remove from heat and let it cool slightly.

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

In a mixing bowl, whisk together the cooled browned butter, light brown sugar, and white sugar until the mixture is smooth.

Stir in the room temperature egg and vanilla extract until well combined.

In a separate bowl, sift together the all-purpose flour, baking soda, and salt (if using). Gradually fold this mixture into the wet ingredients until just combined.

Gently fold in the chopped dark chocolate and finely chopped pistachios.

Use a cookie scoop or tablespoon to portion the dough onto the prepared baking sheet, leaving space between each scoop.

Place the cookies in the oven and bake for 10-12 minutes, or until the edges turn golden brown and the centers appear slightly underbaked.

Remove the cookies from the oven, sprinkle flake sea salt on top while they are still warm, and then let them cool before transferring to a wire rack.