Preheat oven to 375F°. Line baking sheet with parchment paper.
In a medium bowl, combine flour, cocoa powder, baking powder, and salt.
Add pistachios, and mix.
In a mixer, mix butter and sugar on medium speed for 1-1/2 minutes.
Add eggs, one at a time.
Add the dry ingredients and mix on low speed until just combined to make a dough.
Remove the dough and using your hands, divide the dough into two or three pieces and form into long flat shapes about 8" long x 1-1/2 inches wide.
Place on the lined baking sheets and bake 20 minutes.
When cool enough to handle, gently cut the loaves on the angle into 1/2 inch slices (a serrated bread knife works best). Return to the baking sheet fitting as many as you can on the baking sheet, you may need to do this in batches.
Bake the biscotti for another 3-4 minutes on each side, less if you like it softer. Makes about 24.