Melt 1 sticks butter in a saucepan or in the microwave. Let it cool for 3-5 minutes.
Pour the butter in to a large mixing bowl. Add 125 grams brown sugar and 40 grams white sugar. Whisk vigorously until the mixture is smooth, thick, and glossy (about 1 minute).
Add 1 large egg and 1 teaspoon vanilla extract and mix until fully incorporated.
In a separate bowl, whisk together 120 grams flour, ½ teaspoon baking soda, ¼ teaspoon baking powder, and ⅙ teaspoon kosher salt. Fold dry ingredients into wet just until a few streaks remain.
Stir ½ cup semi-sweet chocolate chunks and ¼ cup unsalted pistachios.
Cover the dough and chill it for at least 30 minutes.
Heat your oven to 350°F. Line your baking sheets with parchment paper or silicon mats for easy cleanup and to prevent sticking. .
Scoop 2 tablespoon portions of dough onto the prepared tray.
Bake at 350°F for 11–13 minutes, until edges are golden brown and centers are puffed but soft. Halfway through the baking time, bang ther pan on the rack to deflate the cookies and encourage crackled tops.
Sprinkle with flaky sea salt while warm. Cool 5 minutes on the pan before transferring to a wire cooling rack.