Preheat oven at 325F. Lightly grease cookie sheet or line with parchment paper, set aside. In a large mixing bowl combined flour, baking powder, salt and sugar, mix a well in the center of the flour mixture , place eggs and yolks, stir into flour mixture. Add melted butter, and if desired add orange or lemon peels, stir until dough forms a ball. Stir in almonds or hazelnuts. Turn dough unto a lightly floured surface, divide dough into 3; shape into a 14" long logs. Place 3" apart on the prepared cookie sheet, flatten logs slightly until 1 1/2" wide. Bake 25 - 30 minutes or until firm & lightly brown. Remove from oven and place cookie sheet on wire rack, cool 15 minutes. Transfer logs to cutting board, using a serrated knife to cut diagonally into 1/2" slices; place cut side down on cookie sheet. Bake 10 minutes, turn over and bake other side for 10 - 15 minutes more or until crisp and dry, golden brown. Optional dip or drizzle white chocolate or milk chocolate on biscotti To make icing place 6 ozs chocolate and shortening in a small bowl and microwave on medium power for 1 - 2 minutes, stirring twice, drizzle or dip one end of biscotti and place on waxpaper until chocolate sets. Transfer biscotti to a wire rack until completely cool. Store in airtight container. Makes 24 Biscotti.