Preheat oven to 350° and line a cookie sheet with parchment or a Silpat. Sift the flour, sugar, cocoa powder, baking soda and salt into the bowl of your mixer. With the paddle attachment, mix in the eggs, one at a time on low speed. Add the chocolate, nuts, ginger and candied grapefruit. Mix until everything is well distributed. The dough will be very sticky.
Scoop the dough out with a Bowl Scraper or Rubber Spatula onto the silpat or parchment. Divide the dough in half. Using wet hands form the two halves into logs. You want the logs to be as even as possible from one end to the other.
Bake for 30+ minutes or until the logs are firm to the touch. Allow them to cool for about 25 minutes. If the logs are still too warm they will fall apart when you try to slice them.
Slice the logs into 1/2 thick slices with a serrated Knife. Line them up on the silpat and bake them for 15 minutes. Flip them over and bake for an additional 10 minutes. If you like your biscotti slightly softer, then reduce the baking by about 10 minutes. If you do this they will not store quite as long. If baked until dry they will store for several days.
