In a large bowl using a handheld mixer or stand mixer fitted with a paddle attachment, beat the butter and brown sugar together on medium-high speed until combined and creamy, about 2 minutes. Beat in egg and vanilla extract on high speed. Scrape down the sides and bottom of the bowl as needed, and continue to beat until fully combined. On low speed, beat in the flour and salt until combined. The cookie dough will be thick and slightly sticky. Switch to high speed and beat in most of the chocolate (leave a few chunks aside for step 4) and 2/3 cup of the pistachios until combined.

Turn the dough out onto a floured work surface and, with floured hands, divide or cut into two. Shape each half into an 8-inch log, about 2.5 inches in diameter. The measurements don’t have to be exact. Roll each log in a mix of coarse sugar and the leftover pistachios. Tightly wrap the logs in plastic wrap and chill in the refrigerator for at least 3 hours and up to 5 days. Chilling is mandatory for this cookie dough. I prefer to chill mine for 4 hours or even overnight—the colder the dough, the thicker the cookies.

Preheat oven to 350°F (177°C). Line two large baking sheets with parchment paper or silicone baking mats. (Always recommended for cookies.) Set aside.

Slice each log into 12 equally thick cookies and place cookies on baking sheets about 2 inches apart. (The chocolate chunks in the cookie dough will be very hard and may not slice, leaving gaps in some cookies. Press any extra chunks you set aside in step 1 into the tops, if needed.) If desired, sprinkle each with sea salt.

Bake the cookies for 12-14 minutes or until brown around the edges. Remove from the oven and allow cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.

Cookies will stay fresh covered at room temperature for 1 week.