½ cup unsweetened cocoa powder (Ghirardellie or Hershey's Special Dark will work)
¾ tsp kosher salt (option if using salted, roasted pistachios)
¼ tsp baking soda
1¼ cups (2½ sticks) unsalted butter, room temperature
1¼ cups (lightly packed) light brown sugar
1 tsp vanilla extract
1 large egg white
5 oz. bittersweet or semisweet chocolate, chopped
1 cup unsalted, shelled raw pistachios, coarsely chopped
Flaky sea salt (such as Maldon)
Instructions
Sift together flour, cocoa powder, kosher salt, and baking soda in a medium bowl.
In the bowl of a stand-mixer, beat butter, brown sugar, and vanilla on high speed until light and fluffy. It will take about 4 minutes.
Gradually add dry ingredients while mixing on low just to combine.
Add egg white and mix on low to combine as well.
Fold in chocolate and pistachios with a spoon.
Divide dough into 4 pieces and roll each into a ball. Roll each piece into an 8”-long log about 1½” in diameter. If it feels crumbly, mush the dough together more firmly. Wrap tightly in parchment paper and chill until firm, at least 4 hours. (The colder your dough, the easier it will be to slice. If you're rushed for time, you can also use the freezer.)
Preheat to 350°. Working with 1 log of dough at a time and using a serrated knife, cut logs into ¼”-thick rounds and transfer to a parchment-lined baking sheet, spacing ½” apart.
Sprinkle cookies with sea salt and bake, rotating baking sheet halfway through, until set around edges and centers look dry, 10–15 minutes.
Transfer to wire racks and let cool.
Recipe by StreamingGourmet at http://blog.streaminggourmet.com/2013/12/25/chocolate-pistachio-sables-via-bon-appetit-a-guest-post/