Preheat oven at 375F. Lightly grease ex-large cookie sheet or line with parchment paper; set aside. In a large mixing bowl beat butter with electric mixer on medium speed for 30 seconds, add sugar, cocoa powder and baking powder, beat until combined. Beat in eggs and as much flour as you can with the mixer. Stir in remaining flour with a wooden spoon and stir in white and semisweet chocolate chunks and add (optional) chopped cashews Divide dough in half, shape each into 9" long loaf. Place 4" apart on prepared cookie sheet, flatten slightly to 2" wide. Bake in oven for 20 - 25 minutes or until tooth pick inserted in center of loaf comes out clean. Cool on cookie sheet on wire rack for 15 minutes. Reducing temperature in oven to 325F. Placing loaves on cutting board, using a serrated knife to cut diagonally 1/2" slices. Place slices cut side down on the cookie sheet. Bake in reduced oven for 8 minutes, turn slices over and bake for 7 - 9 minutes more or until dry and crisp(do not over bake). Cool Biscotti and if add white or semisweet chocolate drizzle or dip. To make icing, place 4 oz of white or semisweet chocolate and shortening in a small bowl and microwave on medium power for 1-2 minutes, stirring twice you can drizzle on biscotti or dip one end of the biscotti and place a cashew on chocolate and place biscotti on waxpaper to set the dip or drizzle. Store in an airtight container. Makes 32 Biscotti.