PREPARATION:
- Melt chocolate in top of double boiler over hot, not boiling, water. Remove from heat; cool. Beat butter and 1 cup powdered sugar in large bowl until well blended. Add egg yolks, vanilla and melted chocolate; beat until light. Blend in flour to make stiff dough. Divide dough into 4 parts. Shape each part into log about 1-1/2 inches in diameter. Wrap each log in plastic wrap; refrigerate until firm, at least 30 minutes or up to 2 weeks. (For longer storage, freeze up to 6 weeks.)
- Preheat oven to 350°F. Line cookie sheets with parchment paper or leave ungreased. Cut rolls into 1/8-inch-thick slices; place 2 inches apart on cookie sheets. Bake 8 to 10 minutes or just until set but not browned. Remove to wire racks to cool.
- Spread desired amount of softened ice cream on bottoms of half the cookies. Top with remaining cookies, flat sides down, to make sandwiches. Dust tops with powdered sugar; serve immediately.
