Roll pastry into a 15x 23 cm rectangle. Cut into 9 (15x 3 cm) strips. Starting at tip of mold, wrap one strip around an ungreased 10 cm metal cream horn mold, winding strip spiral-fashion and overlapping edges about 1 cm. Place on lightly greased baking sheet, end of strip down. Repeat with remaining strips. Combine egg yolk and water; brush over entire pastry. Freeze 10 minutes. Bake at 220ºC or 10 to dozen minutes or until puffed and golden brown. Remove from oven, and gently slide molds from pastry. Turn oven off. Return pastry to oven for 10 minutes. Remove from oven, and cool completely on a wire rack. Combine whipping cream and powdered sugar; beat at high speed of an electric mixer until soft peaks form. Spoon whipped cream into a decorating bag fitted with metal tip No. 4B. Pipe whipped cream into pastry horns. Sprinkle grated chocolate over tops of cream horns. Chill until NOTE: One-half (17- 0.25-ounce) package frozen puff pastry may be substituted for half recipe Basic Puff Pastry. ----