1In medium bowl, mix powdered sugar, butter, vanilla and egg with spoon. Stir in flour and salt. Divide dough in half. Stir cocoa into one half of dough; stir ground hazelnuts into other half of dough.
2Roll half of each dough on waxed paper into 11x7-inch rectangle. Place hazelnut dough on cocoa dough; peel off waxed paper. Roll doughs together to 3/16-inch thickness. Roll up rectangle tightly, beginning at 11-inch side, using waxed paper to help lift. Pinch edge of dough into roll to seal. Wrap and refrigerate at least 4 hours until firm. Repeat with remaining dough.
3Heat oven to 375ºF. Cut rolls into 1/4-inch slices. Cut each slice into fourths. Place pieces 1 inch apart on ungreased cookie sheet. Bake 5 to 6 minutes or until set. Immediately remove from cookie sheet to wire rack. Cool completely.
4Dip curved edge of each cookie into melted chocolate, then dip into chopped hazelnuts. Place on waxed paper until chocolate is firm. Store tightly covered or freeze.