Preheat oven 375F. Lightly grease cookie sheet or line with parchment paper, set aside. Beat butter in a large mixing bowl with a electric mixer on medium to high for 30 seconds. Add brown sugar, baking powder and salt. Beat until combined, scraping sides of bowl occasionally. Beat in eggs and cocoa powder and beating in as much as flour as you can with the mixer. Stir in remaining flour and nuts with a wooden spoon and the 4ozs of bittersweet chocolate. Divide the dough in half,shape each portion into 9" rolls. Place rolls on prepared cookie sheet, flatten each roll to 2" wide. Bake in preheated oven for 20 - 25 minutes or until a wooden pick in the center comes out clean. Cool on cookie sheet for 15 minutes. Reduce oven to 325F. Cut each roll diagonally in 1/2" thick slices, with a serrated knife. Place slice, cut side down on the cookie sheet. Bake in oven for 8 minutes. Carefully turn slice over and bake for 7 - 9 minutes more or until dry and crisp. Transfer to a wire rack to cool for 1 hour. Makes 2 dozen biscotti. Microwave the 6 ozs of special dark chocolate and shortening in a small bowl on half power for 1 - 2 minutes or until melted , stirring twice. Dip one end of each biscotti, let excess drip in bowl. Place biscotti on waxpaper,let stand until set. NOTE: To toast nuts, spread nuts in a shallow pan in a single layer. Bake for 4 - 5 minutes or until golden brown, stirring once or twice. Wrap warm nuts in a clean tea towel, rub nuts in towel to remove skins, cool completely. Chop nuts and set aside.