1. In blender at medium speed or in food processor with knife blade attached, finely chop filberts. Remove 1/4 cup chopped filberts to small bowl; set aside.
2. In large bowl, with mixer at high speed, beat butter or margarine and sugar until light and fluffy. Reduce speed to low; add flour, vanilla, egg, and remaining chopped filberts. Beat ingredients until well mixed, occasionally scraping bowl with rubber spatula.
3. Preheat oven to 400°F. Spoon some of the dough into decorating bag with medium-sized rosette tube. Pipe dough in 2 1/2-inch lengths, about 1 inch apart, onto ungreased large cookie sheet.
4. Bake cookies 6 to 8 minutes until golden. With pancake turner, carefully remove cookies to wire racks to cool completely. Repeat with remaining dough.
5. When cookies are cold, in heavy 1-quart saucepan over low heat, heat semisweet-choco-late squares, stirring occasionally, until melted and smooth.
6. Dip 1/2 inch of each end of a cookie into melted chocolate; gently scrape off excess chocolate across rim of saucepan. Lightly sprinkle chocolate-dipped ends of cookie with some reserved chopped filberts.
7. Place cookie on waxed paper; let chocolate dry. Repeat with remaining cookies, chocolate, and chopped filberts. Store cookies in tightly covered container.