The secret to the super-crisp texture here is cutting the dough into very thin rounds; coarse sanding sugar on top adds to their crunch.
Source: Holiday Cookies 2005, Special Issue Holiday 2005
Yield Makes about 4 dozen
1 1/2 cups all-purpose flour
1/2 cup unsweetened Dutch-process cocoa powder
1 1/2 teaspoons instant espresso powder
1/2 teaspoon coarse salt
1 cup (2 sticks) unsalted butter, softened
1 cup confectioners' sugar
1 teaspoon finely grated orange zest
1 teaspoon pure vanilla extract
Coarse sanding sugar, for sprinkling
Sift together flour, cocoa powder, espresso powder, and salt into a medium bowl; set aside.
Put butter, confectioners' sugar, orange zest, and vanilla in the bowl of an electric mixer fitted with the paddle attachment. Mix on medium speed until pale and fluffy, about 3 minutes. Reduce speed to medium-low, and gradually add flour mixture until just combined.
Transfer dough to a 12-by-16-inch piece of parchment; shape into a log. Roll in parchment to 1 1/2 inches in diameter, pressing a ruler along edge of paper at each turn to narrow the log and force out air. Transfer in parchment to a paper towel tube; chill at least 2 hours or overnight.
Preheat oven to 350 degrees. Cut log into 1/4-inch-thick slices; transfer to baking sheets lined with parchment paper. Brush tops with water; sprinkle with sanding sugar. Bake until set, 15 to 17 minutes. Cool on sheets on wire racks. Store in airtight containers at room temperature up to 1 week.