1. Melt 4 tablespoons of the butter and stir in the cocoa and espresso powder until it forms a smooth paste. Let sit for 15 minutes to cool.
2. In the bowl of a stand mixer, combine the sugar, salt, remaining butter and chocolate paste. Mix on high speed until fluffy, about 1 minute, scraping down sides when necessary. Add yolks and vanilla and mix at medium speed for 30 seconds. Scrape down sides of the bowl.
3. Run mixer at low and add flour in three additions, making sure mixture is combined before adding next addition, and scraping down bowl between additions.
4. Turn dough onto counter and divide into 3 four-inch disks. Wrap in plastic wrap and chill in the refrigerator for at least an hour.
5. Preheat oven to 375 degrees. Roll out dough disk to 1/8-inch thick between cling wrap (on the bottom) and a sheet of parchment paper (on the top). (Alternatively, you can roll the dough between two sheets of parchment paper, but I find this impossible to keep from sliding around on the counter top.) Turn the rolled-out dough over, so the parchment paper is on the bottom and the cling wrap is on the top. Peel off the cling wrap and cut the dough into shapes using cookie cutters. If you want to add walnuts (as I've done-- it's an easy way to decorate the cookie), place on the cookies before baking.
6. Bake on a cookie sheet lined with parchment paper for 8-10 minutes, rotating baking sheet halfway through baking. Make sure not to overbake-- do not let the cookies become too dark on the edges. Cool on cookie sheet for 5 minutes, then transfer to a cooling rack. When cool you can glaze or decorate with melted white chocolate.

Labels: recipes, the chocolatey, the sweet