Preheat oven to 350°F. Line two baking sheets with parchment paper or a silicone baking mat. Set them aside.
Cream together the softened butter, granulated sugar, and dark brown sugar for 1-2 minutes until fluffy. Add in the egg and vanilla extract and mix until combined.
Add in the flour, baking soda, and salt and mix until everything is combined. Fold in the chopped pistachios and chocolate chunks.
Use a medium cookie scoop to scoop the dough. Roll each scoop into a ball and place a few inches apart on the prepared baking sheets.
Bake for 11-13 minutes. Cookies will still look a bit soft in the center, but that is what you want. Allow the cookies to cool on the baking sheets for a few minutes, then carefully transfer them to a cooling rack. Enjoy them as is or top them with flaky sea salt.