VANILLA-AND-CHOCOLATE SHORTBREAD SWIRLS

Steps:

• In a medium bowl, whisk together flour and salt.
• In the bowl of a stand mixer fitted with the paddle attachment, cream together butter, confectioners' sugar, and vanilla on medium speed until light and fluffy, about 2 minutes. Stop mixer and add flour mixture; mix on low speed until just combined. Remove half the dough; divide into two equal pieces, wrap in plastic, and set aside while you make the chocolate dough.
• In a small bowl, stir together cocoa, espresso, and 2 tablespoons hot water. Add cocoa mixture to remaining cookie dough and mix on low speed until color is uniform, scraping down sides of bowl as needed.
• Place half the chocolate dough on a sheet of parchment and cover with a sheet of plastic wrap. Roll dough into a 14-by-10-inch rectangle (dough will be very thin but can be easily patched if it tears). Set aside, still covered with plastic. Repeat rolling process with remaining chocolate dough and both pieces of vanilla dough.
• Place one sheet of chocolate dough on work surface and remove plastic. Remove plastic from one sheet of vanilla dough and invert, still attached to its parchment backing, onto chocolate dough, pressing gently with the palm of your hand to adhere. Gently peel back parchment paper to remove. Continue layering with remaining chocolate and vanilla doughs. Position dough with one short side parallel to edge of work surface, then roll dough into a tight spiral. Wrap log in parchment and place in a cardboard paper-towel tube that has been cut open from end to end (this will help retain the round shape of the log of dough). Refrigerate until firm, at least 1 hour or overnight.
• Preheat oven to 325 degrees. Line two rimmed baking sheets with parchment. Trim ends from dough. Slice dough 1/4 inch thick. Roll each cookie between sheets of parchment into an oblong disk about 3 inches long and 1/8 inch thick; transfer to prepared sheets. Bake until crisp, 8 to 10 minutes. Transfer sheets to wire racks and let cool completely. Working with one cookie at a time, dip an edge in melted chocolate and coat with pistachios. Transfer to fresh parchment-lined baking sheets and let stand until chocolate is set, 45 to 60 minutes.