Instructions: Preheat the oven to 350 F. Grease several baking sheets and set aside. In a small bowl, stir together the egg yolk and coffee powder. Let stand for about 5 minutes, or until the coffe dissolves. In a large mixing bowl, beat the butter with an electric mixer on medium speed until very light.

Add sugar, cocoa powder, and egg yolk-coffee mixture and beat until very fluffy and smooth. Gradually beat in flour until thoroughly incorporated but not overmixed. Stir in grated chocolate until evenly distributed throughout. Fit a large pastry bag with a large (3/8-inch diameter) star tip. Stand the bag, tip down, in a tall glass and fold down the top of the bag about 3 1/2 inches. Spoon in enough dough to fill it two-thirds full.

Unfold the cuff and tightly twist the top to close it. Pipe 1 1/4-inch diameter rosettes onto a baking sheet, spacing about 1 1/2 inches apart.

(You can also use a cookie press fitted with a star-shaped disk to make these cookies.) Place baking sheets in center of the oven and bake the cookies for 8 to 10 minutes, or until slightly firm on top. Remove baking sheets from the oven and let the cookies stand for 2 to 3 minutes. Then transfer them to wire racks and let stand until cooled completely. Lightly dust the cookies with powdered sugar just before serving, if desired. Store in an airtight container for up to a week. Freeze for longer storage.

If you would like to email yourself the recipe for later use, or share the recipe with your friends or family, enter the email addresses below and this recipe will be emailed to you and others as well.