Combine flour, cocoa powder, baking powder, salt and sugar in a large bowl.
Add chocolate chips and mix.
Gradually add eggs and egg whites to the mixture and combine to make a dough. (If dough is too dry add one more egg white)
Divide the dough into two or three loafs.
Place on the lined baking sheets and bake 20 minutes. (If the dough is too sticky to form with your hands, you can use a wooden spatula to transfer it onto the baking sheets)
When cool enough to handle, gently cut the loaves on the angle into 1/2 inch slices (a serrated bread knife works good for this).
Return to the baking sheets fitting as many as you can. You may need to do this in batches.
Bake the biscotti for another 3-4 minutes on each side. (less time for if you like it softer)