Direction :

1. Place the flour in a medium bowl, sift in the cocoa and baking soda, and whisk to combine.
2. Place the butter in the bowl of a stand mixer fitted with the paddle attachment. Turn to medium-low speed and mix until smooth. Add the salt and mix for another 15 to 30 seconds. Add the sugar and mix for about 2 minutes, until fluffy. Scrape down the sides and bottom of the bowl.
3. Add the dry ingredients in 2 additions, mixing on low speed for 15 to 30 seconds after each, or until just combined, then mix until the dough begins to come together.
4. Mound the dough on the work surface and, using the heel of your hand or a pastry scraper, push it together into a 6-inch-square block. Note: I like to cut this block in half and wrap each half separately — I find it easier to roll out half a block at a time. Wrap in plastic wrap and refrigerate for at least 1 hour, until firm. (The dough can be refrigerated for up to 2 days or frozen for up to 1 month.)
5. Place oven rack in middle of oven and preheat the oven to 325°F. Line two sheet pans with Silpats or parchment paper.
6. Unwrap the dough and place it between two pieces of parchment paper or plastic wrap. With a rolling pin, pound the top of the dough, working from left to right, to begin to flatten it, then turn the dough 90 degrees and repeat (this will help prevent the dough from cracking as it is rolled). Roll out to a 1/8-inch-thick sheet. If the dough has softened, slide it (in the parchment) onto the back of a sheet pan and refrigerate until firm enough to cut.
7. Using a 2.5-inch fluted cutter, cut rounds from the dough. Note: I get 12 rounds from each half of dough, for a total of 24 rounds. With the scraps, you can do two things: 1. push them together, refrigerate until firm, and reroll/cut or 2. bake them as is, let them cool and grind in the food processor to use as cookie crumbs over ice cream. If the dough softens, return to the refrigerator until the cookies are firm enough to transfer to a sheet pan. Note: I find the easiest way to release them from the scraps is to slide my hand underneath the parchment paper and push up with even force underneath the cut cookie — hope that makes sense. Arrange the rounds on the sheet pans, leaving about one inch between them.
8. Bake for 5 minutes. Set the pans on a cooling rack and let cookies cool completely on pans.
9. To assemble the sandwiches, slide a flat spatula underneath each cookie to release it from the parchment. Cookies will be delicate, so be gentle. Flip half of the cookies over. Drop a scoop of vanilla ice cream over the turned over cookies. Top with another cookie using a delicate hand — gently press down from the middle of the cookie to prevent cookies from breaking. Wrap each sandwich in plastic wrap and freeze until ready to serve. If ice cream has gotten too soft, place whole sheet pan of sandwiches in freezer for 20 minutes, then wrap each individually for storage. Freeze for at least one hour before serving. Will keep for days in the fridge.