These creepy cookies can be baked one day ahead of Halloween party. Store them in single layers in airtight containers at room temperature.
Whisk together flour, salt, and espresso in a large bowl; set aside.
Put butter and sugar into the bowl of an electric mixer fitted with the paddle attachment; beat on medium speed until fluffy, about 3 minutes. Beat in vanilla. Beat in flour mixture. Transfer dough to plastic wrap. Flatten into a disk; wrap. Refrigerate until firm, at least 1 hour or overnight.
Preheat oven to 275 degrees. Photocopy the template on this page, and cut it out. On a lightly floured work surface, roll out dough to 1/8 inch thick. Using template and a paring knife, cut dough into 12 headstones. Transfer to a parchment-lined baking sheet. Refrigerate 30 minutes.
Bake cookies until set but not browned, 25 to 30 minutes. Transfer to a wire rack, and let cool completely.
Melt chocolate in a heatproof bowl set over a pan of simmering water, stirring occasionally until smooth. Let stand until cool but not stiff. Transfer to a pastry bag fitted with a very small plain round tip, such as an Ateco #2, or to a parchment-paper cone. Pipe desired design on cookies.
The chocolate can also be melted in a microwave oven. Place chopped chocolate in a glass dish, and microwave on high for two minutes, stirring once halfway through.