Preparation / Directions:
Preheat oven to 350F (175C). Grease 3 or 4 baking sheets. In a bowl, beat butter and sugar until light and fluffy. In another bowl, beat egg with coffee granules until dissolved, then add to creamed mixture gradually, beating well. Sift flour, cornstarch and baking powder over mixture. Stir in to make a soft dough; knead lightly. On a floured surface, roll out dough to a 1/8-inch thickness. Using a 2-inch fluted cutter, cut out cookies and place on prepared baking sheets. Bake in oven 10 to 15 minutes, until firm and lightly browned. Transfer to wire racks to cool. Put cooled melted chocolate into a pastry bag, snip off end and pipe parallel zigzag lines on of cookies.
To make filling, in a bowl, beat butter and powdered sugar until smooth and creamy. In another bowl, mix egg yolk with coffee granules; add to creamed mixture and beat until smooth. Spread filling on plain cookies and sandwich together with decorate cookies. Let stand in a cool place until filling is firm. Makes about 24 cookies.